Systems and methods for preventing spark plug fouling in a variable displacement engine

ABSTRACT

Methods and systems are provided for reducing fouling of a spark plug in a cylinder of a variable displacement engine configured to propel a vehicle. In one example, a method includes in response to deactivation of a cylinder or cylinders of the engine, providing spark to the cylinder or cylinders at a predefined position of a piston or pistons coupled to the cylinder or cylinders, respectively, where the predefined position comprises the piston or pistons being within a threshold of a bottom dead center position. In this way, spark plug fouling may be reduced or eliminated during conditions of cylinder deactivation.

FIELD

The present description relates generally to methods and systems forcontrolling a vehicle engine to reduce spark plug fouling in vehiclescapable of selectively deactivating one or more engine cylinders.

BACKGROUND/SUMMARY

Engines may be configured to operate with a variable number of active ordeactivated cylinders to increase fuel economy, while optionallymaintaining the overall exhaust mixture air-fuel ratio aboutstoichiometry. Such engines are known as variable displacement engines(VDE). In some examples, a portion of an engine's cylinders may bedisabled during selected conditions, where the selected conditions canbe defined by parameters such as a speed/load window, as well as variousother operating conditions including vehicle speed. A VDE control systemmay disable selected cylinders through the control of a plurality ofcylinder valve deactivators that affect the operation of the cylinder'sintake and exhaust valves, or through the control of a plurality ofselectively deactivatable fuel injectors that affect cylinder fueling.By reducing displacement under low torque request situations, the engineis operated at a higher manifold pressure, reducing engine friction dueto pumping, and resulting in reduced fuel consumption.

There are a few examples of how deactivating engine cylinders istypically conducted in a four-stroke engine that includes intake,compression, combustion (power), and exhaust strokes. In a firstexample, during the intake stroke an air-fuel charge is drawn into thecylinder, the air-fuel charge is compressed, spark is provided resultingin combustion, but rather than exhausting the combustion gases, theexhaust valve is maintained closed. This traps the high-pressure chargein the cylinder. An advantage to this methodology is lower oilmigration/consumption as the high pressure in the deactivated cylinderprevents migration of oil into the cylinder. However, such a method hasa distinct disadvantage in that there is a noticeable torque bump atdeactivation, and a pumping penalty is realized for the first eventafter deactivation (which is small if deactivating for short periods,but significant if deactivated and reactivated often).

Another example of cylinder deactivation includes the same steps asabove in the first example, but rather than trapping the high-pressurecharge, the cylinder is exhausted, but rather than re-inducting anintake charge after the exhaust stroke, a vacuum is trapped in thecylinder by closing the exhaust valve (while maintaining closed theintake valve). Such an example has an advantage over the first example,in that there is a reduction in noticeable torque bump at deactivation,and increased fuel efficiency when deactivated and activated often, dueto lower pumping work. However, a distinct disadvantage to suchmethodology is that by trapping the vacuum in the cylinder, oilconsumption may increase. Increased oil consumption may result in atleast two undesirable issues. The first may include oil fouled sparkplug(s). A second issue may include the fact that crankcase vaporsand/or oil migrating from a crankcase to the cylinder may result in acombustible mixture, which may result in a combustion event in thecylinder. Disabling spark during cylinder deactivation may preventunintended combustion of crankcase vapors/oil migration, however oilfouling and oil migration may still result in spark plug degradation(spark plug fouling).

U.S. Pat. No. 9,261,067 B2 teaches a method for reducing spark plugfouling in deactivated cylinder(s), comprising supplying spark at aparticular determined instance while the cylinder(s) are deactivated.However, the inventors have recognized an issue with such an approach.For example, the supplying of spark is not specified with relation toengine cycle status, or position of a piston(s) coupled to thecylinder(s). As such, providing spark according to U.S. Pat. No.9,261,067 B2 may result in undesired combustion events while thecylinder(s) is deactivated.

Thus, the inventors herein have developed systems and methods to atleast partially address the above-mentioned issues. In one example, amethod comprises reducing fouling of a spark plug in a cylinder of anengine configured to propel a vehicle by providing a spark to thecylinder after the cylinder has been deactivated, where the spark isprovided when a piston coupled to the cylinder is within a threshold ofbottom dead center. By providing spark when the piston is within thethreshold of bottom dead center, undesired combustion events may bereduced or eliminated, while spark plug fouling may additionally bereduced or eliminated.

As one example, the engine may comprise a variable displacement engine,and where providing the spark to the cylinder after the cylinder hasbeen deactivated occurs in response to the cylinder being deactivatedvia trapping a negative pressure with respect to atmospheric pressure inthe cylinder at deactivation. In such an example, trapping the negativepressure at deactivation may include exhausting a combusted mixture ofair and fuel to an exhaust system of the engine, and then sealing thecylinder from atmosphere.

In examples where a plurality of cylinders are selected fordeactivation, such a method as that described above may includeproviding spark to the plurality of cylinders in response todeactivation of the plurality of cylinders, at the predefined positionof a plurality of pistons coupled to the plurality of cylinders.

In some examples of such a method, a spark ignition energy comprisingthe spark provided to the cylinder after deactivation of the cylinder,is variable. For example, spark ignition energy may be increased after apredetermined number of spark events, while the cylinder is deactivated.Furthermore, in some examples, a spark frequency of the spark providedto the cylinder may be variable as a function of vehicle operatingconditions.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an example variable displacement enginesystem.

FIG. 2 shows a partial engine view.

FIG. 3A shows an example method for selecting a cylinder deactivationstrategy, and for conducting cylinder deactivation via trapping vacuumin a cylinder selected for deactivation.

FIG. 3B shows an example method that continues from FIG. 3A, andincludes conducting cylinder deactivation via trapping a high-pressurecharge in a cylinder selected for deactivation.

FIG. 4 shows an example map for deactivating an engine cylinderaccording to the method of FIG. 3A.

FIG. 5 shows another example map for deactivating an engine cylinderaccording to the method of FIG. 3A.

FIG. 6 shows another example map for deactivating an engine cylinderaccording to the method of FIG. 3A.

FIG. 7 shows an example map for selectively deactivating an enginecylinder according to the method of FIG. 3A and FIG. 3B, depending on anindicated oil quality.

FIG. 8A shows an example method for selecting a cylinder deactivationstrategy, for conducting cylinder deactivation via trapping vacuum in acylinder selected for deactivation, and for mitigating a torque bumpresulting from an unintended combustion event.

FIG. 8B shows an example method that continues from FIG. 8A, andincludes conducting cylinder deactivation via trapping a positivepressure in a cylinder or cylinders selected for deactivation, andmitigating a torque bump resulting from an unintended combustion event.

FIG. 9 depicts an example map for reactivating a deactivated cylinder inresponse to an indication of unintended combustion in the deactivatedcylinder.

FIG. 10 depicts an example timeline for reducing or avoiding a torquebump resulting from unintended combustion in a deactivated cylinder, andfor reassigning activated/deactivated cylinders subsequent to theunintended combustion event.

DETAILED DESCRIPTION

The following description relates to systems and methods for reducingspark plug fouling in a vehicle with a variable displacement engine(VDE), such as the engine depicted at FIG. 1. Such an engine may becapable of selectively deactivating one or more engine cylinders, suchas the engine cylinder depicted at FIG. 2. Two methods may be utilizedto deactivate an engine cylinder in response to conditions being met fora cylinder deactivation event, or VDE event. In one example, ahigh-pressure charge may be trapped in a cylinder selected fordeactivation. Trapping a high-pressure charge may reduce oil migrationto the cylinder while the cylinder is deactivated, thus preventing sparkplug fouling. However, such an approach may result in an undesirabletorque bump at deactivation. Furthermore, such an approach may result ina pumping penalty, which may be significant if the cylinder isdeactivated and reactivated often. In another example, a vacuum may betrapped in the cylinder selected for deactivation. Trapping a vacuum mayreduce or avoid the torque bump that would otherwise be present atdeactivation (if a high-pressure charge were trapped in the selectedcylinder). However by trapping a vacuum, oil migration to the selectedcylinder may increase. Such increased oil migration may result in sparkplug fouling in some situations. To prevent such spark plug fouling,spark may be provided to a deactivated cylinder or cylinders withtrapped vacuum, where the spark is provided when a piston coupled to thecylinder is near bottom dead center (BDC) (e.g. within a thresholdpercentage of degrees from BDC). Accordingly, FIG. 3A depicts a methodwhere it may be determined whether to conduct a cylinder deactivationvia trapping vacuum, or trapping high-pressure charge. Such adetermination may be a function of an indicated oil quality, forexample. FIG. 3A further depicts controlling spark during the cylinderdeactivation, provided the cylinder is deactivated with a vacuum trappedin the cylinder. Alternatively, if it is indicated at FIG. 3A that it ispreferable to conduct deactivation of the cylinder via trapping thehigh-pressure charge, FIG. 3B depicts such a method. FIG. 4 depicts amap where spark is provided to a cylinder near BDC at every occasion(e.g. twice per engine cycle) the piston coupled to the cylinder is nearBDC. Alternatively, FIG. 5 depicts a map where spark is provided to acylinder near BDC at every other occasion (e.g. once per engine cycle)the piston is near BDC. Furthermore, FIG. 5 depicts an example where,after two spark events when the piston is near BDC, where the two sparkevents comprise a basal spark ignition energy, spark energy is increasedfor each subsequent spark event. FIG. 6 shows yet another map wherespark is provided to a deactivated cylinder at every occasion a pistoncoupled to the deactivated cylinder is near BDC, where the basal sparkignition energy is provided for a predetermined number of engine cyclesor spark events, and where after the predetermined number of enginecycles (or spark events) elapses, then spark ignition energy isincreased for the remainder of the time the cylinder is deactivated.FIG. 7 depicts still another map where a cylinder is deactivated firstby trapping a vacuum in the cylinder, and where spark is provided nearBDC while the cylinder is deactivated to prevent spark plug fouling, andthen at a later time in the same drive cycle, the cylinder isdeactivated by trapping a high-pressure charge in the cylinder.Determining whether to deactivate the cylinder by trapping a vacuum, ortrapping a high-pressure charge, may be based on a quality of engineoil, for example.

By providing spark to deactivated cylinder(s) near BDC, unintendedcombustion events may be reduced for deactivated cylinders. However, itis herein recognized that such unintended combustion events may, in someexamples and under some circumstances, still occur. Accordingly, turningto FIG. 8A, it depicts an example methodology for reducing or avoiding atorque bump resulting from unintended combustion in a deactivatedcylinder, when the cylinder is deactivated via trapping negativepressure with respect to atmospheric pressure in the cylinder. FIG. 8Bdepicts similar methodology under conditions where a positive pressurewith respect to atmospheric pressure is trapped in the cylinder. FIG. 9depicts an example map for reactivating a deactivated cylinder inresponse to such an unintended combustion event. FIG. 10 depicts anexample timeline for mitigating a torque bump resulting from theunintended combustion event, and for reassigning deactivated cylindersto be reactivated while reassigning activated cylinders to bedeactivated, responsive to an unintended combustion event while theengine is operating in a variable displacement engine mode (VDE mode).

FIG. 1 shows an example variable displacement engine (VDE) 10 having afirst bank 15 a and a second bank 15 b. In the depicted example, engine10 is a V6 engine with the first and second banks each having threecylinders. However, in alternate embodiments, the engine may have adifferent number of engine cylinders, such as 4, 8, 10, 12, etc. Engine10 has an intake manifold 16, with throttle 20, and an exhaust manifold18 coupled to an emission control system 30. Emission control system 30includes one or more catalysts and air-fuel ratio sensors, such asdescribed with regard to FIG. 2. As one non-limiting example, engine 10can be included as part of a propulsion system for a passenger vehicle.

During selected conditions, such as when the full torque capability ofthe engine is not needed, one or more cylinders, such as one of a firstor second cylinder group, may be selected for deactivation (herein alsoreferred to as a VDE mode of operation). Specifically, one or morecylinders may be deactivated by shutting off respective fuel injectorswhile commanding intake and exhaust valves closed. While fuel injectorsof the disabled cylinders are turned off, the remaining enabledcylinders continue to carry out combustion with fuel injectors activeand operating. To meet torque requirements, the engine may produce thesame amount of torque on those cylinders for which the injectors remainenabled. This may require higher manifold pressures, resulting inlowered pumping losses and increased engine efficiency. Also, the lowereffective surface area (from only the enabled cylinders) exposed tocombustion reduces engine heat losses, improving the thermal efficiencyof the engine. In alternate examples, engine system 10 may havecylinders with selectively deactivatable intake and/or exhaust valveswherein deactivating the cylinder includes deactivating the intakeand/or exhaust valves.

Cylinders may be grouped for deactivation in a bank-specific manner. Forexample, in FIG. 1, the first group of cylinders may include the threecylinders of the first bank 15 a while the second group of cylinders mayinclude the three cylinders of the second bank 15 b. In an alternateexample, instead of one or more cylinders from each bank beingdeactivated together, two cylinders from each bank of the V6 engine maybe selectively deactivated together. In still another example, only onecylinder may be deactivated.

Engine 10 may operate on a plurality of substances, which may bedelivered via fuel system 8. Engine 10 may be controlled at leastpartially by a control system including controller 12. Controller 12 mayreceive various signals from sensors 4 coupled to engine 10, and sendcontrol signals to various actuators 22 coupled to the engine and/orvehicle.

Fuel system 8 may be further coupled to a fuel vapor recovery system(not shown) including one or more canisters for storing refueling anddiurnal fuel vapors. During selected conditions, one or more valves ofthe fuel vapor recovery system may be adjusted to purge the stored fuelvapors to the engine intake manifold to improve fuel economy and reduceexhaust emissions. In one example, the purge vapors may be directed nearthe intake valve of specific cylinders. For example, during a VDE modeof operation, purge vapors may be directed only to the cylinders thatare firing. This may be achieved in engines configured with distinctintake manifolds for distinct groups of cylinders. Alternatively, one ormore vapor management valves may be controlled to determine whichcylinder gets the purge vapors.

Controller 12 may receive an indication of cylinder knock orpre-ignition from one or more knock sensors 82 distributed along theengine block. When included, the plurality of knock sensors may bedistributed symmetrically or asymmetrically along the engine block. Assuch, the one or more knock sensors 82 may be accelerometers, orionization sensors. Further details of the engine 10 and an examplecylinder are described with regard to FIG. 2.

FIG. 2 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10. Engine 10 may receive controlparameters from a control system including controller 12 and input froma vehicle operator 130 via an input device 132. In this example, inputdevice 132 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Cylinder (hereinalso “combustion chamber’) 14 of engine 10 may include combustionchamber walls 136 with piston 138 positioned therein. Piston 138 may becoupled to crankshaft 140 so that reciprocating motion of the piston istranslated into rotational motion of the crankshaft. Crankshaft 140 maybe coupled to at least one drive wheel of the passenger vehicle via atransmission system. Further, a starter motor may be coupled tocrankshaft 140 via a flywheel (for example) to enable a startingoperation of engine 10.

Cylinder 14 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 14. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 2 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake passages 142 and 144, and an exhaust turbine 176 arrangedalong exhaust passage 148. Compressor 174 may be at least partiallypowered by exhaust turbine 176 via a shaft 180 where the boosting deviceis configured as a turbocharger. However, in other examples, such aswhere engine 10 is provided with a supercharger, exhaust turbine 176 maybe optionally omitted, where compressor 174 may be powered by mechanicalinput from a motor or the engine. A throttle 20 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 20 may be disposed downstream ofcompressor 174 as shown in FIG. 2, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 178 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhausttemperature may be computed by one or more exhaust gas sensors 128. Itmay be appreciated that the exhaust gas temperature may alternatively beestimated by any combination of temperature estimation methods listedherein.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some embodiments, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Cam actuation system 151 may include firstcamshaft sensor(s) 188. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation system 153may include second camshaft sensor(s) 189. In some examples, one or moreof first camshaft sensor 188 and second camshaft sensor 189 may beutilized to determine piston location, for example whether the piston isat top dead center or bottom dead center, or somewhere in between. Insome examples, such a determination may be provided in conjunction withdata received via the controller from crankshaft position sensor 120. Itmay be understood that in FIG. 2, a camshaft is not shown, but engine 10may include a camshaft. Cam actuation systems 151 and 153 may eachinclude one or more cams and may utilize one or more of cam profileswitching (CPS), variable cam timing (VCT), variable valve timing (VVT)and/or variable valve lift (VVL) systems that may be operated bycontroller 12 to vary valve operation. The position of intake valve 150and exhaust valve 156 may be determined by valve position sensors 155and 157, respectively. In alternative embodiments, the intake and/orexhaust valve may be controlled by electric valve actuation. Forexample, cylinder 14 may alternatively include an intake valvecontrolled via electric valve actuation and an exhaust valve controlledvia cam actuation including CPS and/or VCT systems, or may additionallyinclude the exhaust valve controlled via electric valve actuation. Instill other embodiments, the intake and exhaust valves may be controlledby a common valve actuator or actuation system, or a variable valvetiming actuator or actuation system.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 14 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 14. While FIG. 1shows injector 166 as a side injector, it may also be located overheadof the piston, such as near the position of spark plug 192. Such aposition may improve mixing and combustion when operating the enginewith an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. Fuel may be delivered tofuel injector 166 from a high pressure fuel system 8 including fueltanks, fuel pumps, and a fuel rail. Alternatively, fuel may be deliveredby a single stage fuel pump at lower pressure, in which case the timingof the direct fuel injection may be more limited during the compressionstroke than if a high pressure fuel system is used. Further, while notshown, the fuel tanks may have a pressure transducer providing a signalto controller 12. It will be appreciated that, in an alternateembodiment, injector 166 may be a port injector providing fuel into theintake port upstream of cylinder 14.

It will also be appreciated that while the depicted embodimentillustrates the engine being operated by injecting fuel via a singledirect injector; in alternate embodiments, the engine may be operated byusing two or more injectors (for example, a direct injector and a portinjector, two direct injectors, or two port injectors) and varying arelative amount of injection from each injector.

Fuel may be delivered by the injector to the cylinder during a singlecycle of the cylinder. Further, the distribution and/or relative amountof fuel delivered from the injector may vary with operating conditions.Furthermore, for a single combustion event, multiple injections of thedelivered fuel may be performed per cycle. The multiple injections maybe performed during the compression stroke, intake stroke, or anyappropriate combination thereof. Also, fuel may be injected during thecycle to adjust the air-to-injected fuel ratio (AFR) of the combustion.For example, fuel may be injected to provide a stoichiometric AFR. AnAFR sensor may be included to provide an estimate of the in-cylinderAFR. In one example, the AFR sensor may be an exhaust gas sensor, suchas EGO sensor 128. By measuring an amount of residual oxygen in theexhaust gas, the sensor may determine the AFR. As such, the AFR may beprovided as a Lambda (λ) value, that is, as a ratio of actual AFR tostoichiometry for a given mixture. Thus, a Lambda of 1.0 indicates astoichiometric mixture, richer than stoichiometry mixtures may have alambda value less than 1.0, and leaner than stoichiometry mixtures mayhave a lambda value greater than 1.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Fuel tanks in fuel system 8 may hold fuel with different fuel qualities,such as different fuel compositions. These differences may includedifferent alcohol content, different octane, different heat ofvaporizations, different fuel blends, and/or combinations thereof etc.

Engine 10 may further include a knock sensor 82 coupled to each cylinder14 for identifying abnormal cylinder combustion events. In alternateembodiments, one or more knock sensors 82 may be coupled to selectedlocations of the engine block. The knock sensor may be an accelerometeron the cylinder block, or an ionization sensor configured in the sparkplug of each cylinder. The output of the knock sensor may be combinedwith the output of a crankshaft acceleration sensor to indicate anabnormal combustion event in the cylinder. In one example, based on theoutput of knock sensor 82 in one or more defined windows (e.g., crankangle timing windows), abnormal combustion due to one or more of knockand pre-ignition may be detected and differentiated. As an example,pre-ignition may be indicated in response to knock sensor signals thatare generated in an earlier window (e.g., before a cylinder spark event)while knock may be indicated in response to knock sensor signals thatare generated in a later window (e.g., after the cylinder spark event).Further, pre-ignition may be indicated in response to knock sensoroutput signals that are larger (e.g., higher than a first threshold),and/or less frequent while knock may be indicated in response to knocksensor output signals that are smaller (e.g., higher than a secondthreshold, the second threshold lower than the first threshold) and/ormore frequent.

In addition, a mitigating action applied may be adjusted based onwhether the abnormal combustion was due to knock or pre-ignition. Forexample, knock may be addressed using spark retard and EGR whilepre-ignition is addressed using cylinder enrichment, cylinderenleanment, engine load limiting, and/or delivery of cooled externalEGR.

One or more of fuel injector 166, intake valve 150, and exhaust valve156 may be selectively deactivatable. As discussed at FIG. 1, duringconditions when the full torque capability of the engine is not needed,such as low load conditions, cylinder 14 may be selectively deactivatedby disabling cylinder fueling and/or the operation of the cylinder'sintake and exhaust valves. As such, remaining cylinders that are notdeactivated may continue to operate and the engine may continue to spin.As discussed above, one method of deactivating a cylinder may includetrapping a high-pressure charge in the cylinder, which may prevent oilmigration into the cylinder, but which may result in a noticeable torquebump at the time of deactivation, as well as a pumping penalty for thefirst event after deactivation. Another method of cylinder deactivationmay include trapping a vacuum in the cylinder. Such a method may reducethe torque bump at deactivation, and may increase fuel efficiency whenone or more cylinders are deactivated and activated often, due to lowerpumping work. A disadvantage to trapping a vacuum in the deactivatedcylinder is that oil consumption may increase, which may lead to oilfouled spark plug(s). Furthermore, the vacuum condition may result inoil and/or crankcase vapors from migrating into deactivated cylinder(s),which may result in unintended combustion events. To address such issuesof spark plug fouling, increased oil consumption and/orundesired/unintended combustion events, the inventors herein havedeveloped methods to address them. Such methodology is described indetail below at FIGS. 3A-3B. Briefly, the methodology described hereinmay enable the trapping of vacuum in the deactivated cylinder(s), whichmay in turn reduce the torque bump at deactivation. The methodology mayinclude continuing to provide spark to deactivated engine cylinder(s),but where spark is provided when the piston(s) (e.g. 138) coupled to thedeactivated cylinder(s) are at or near (e.g. within a predeterminednumber of degrees) bottom dead center (BDC). By providing spark nearBDC, the methodology described herein may reduce or eliminate undesiredcombustion events, and may reduce or eliminate spark plug fouling. Morespecifically, by continuing to spark, oil residue may be prevented fromfouling the spark plug. Furthermore, by sparking at BDC, unintendedcombustion events may be reduced or eliminated due to the large cylindervolume at BDC.

Accordingly, discussed herein, BDC may refer to a position of the piston(e.g. 138), which is nearest to the crankshaft (e.g. 140), and top deadcenter (TDC) may refer to a position of the piston farthest from thecrankshaft. For example, it may be understood that BDC is 180° from TDC.By defining BDC in relation to TDC as such, the predetermined number ofdegrees from BDC may readily be determined via the controller (e.g. 12)based on one or more of a camshaft position and/or crankshaft position.

Controller 12 is shown as a microcomputer, including microprocessor unit106, input/output ports 108, an electronic storage medium for executableprograms and calibration values shown as read only memory chip 110 inthis particular example, random access memory 112, keep alive memory114, and a data bus. Controller 12 may receive various signals fromsensors coupled to engine 10, in addition to those signals previouslydiscussed, including measurement of inducted mass air flow (MAF) frommass air flow sensor 122; engine coolant temperature (ECT) fromtemperature sensor 116 coupled to cooling sleeve 118; engine oiltemperature from temperature sensor 187; oil quality from oil qualitysensor 186; a profile ignition pickup signal (PIP) from Hall effectsensor 120 (or other type) (also referred to herein as crankshaftposition sensor) coupled to crankshaft 140; throttle position (TP) froma throttle position sensor; absolute manifold pressure signal (MAP) fromsensor 124, cylinder AFR from EGO sensor 128, and abnormal combustionfrom knock sensor 82 and a crankshaft acceleration sensor. Engine speedsignal, RPM, may be generated by controller 12 from signal PIP. Manifoldpressure signal MAP from a manifold pressure sensor may be used toprovide an indication of vacuum, or pressure, in the intake manifold.

In some examples, engine 10 may include an oil life indicator, or oilquality sensor 186. Oil quality sensor 186 may comprise one or moresensors that may measure conductivity of oil, mechanical properties ofthe oil, soot concentration in the oil, presence and/or amount of waterin the oil, etc. For example, measurement of conductivity may includehow easily electric current passes through the oil, to enable adetermination as to abundance of contaminants in the oil (e.g. lower theresistance, the more contaminants). Measurement of mechanical propertiesmay include a piezoelectric sensor, which may enable determination ofhow thick the oil is.

In some examples, oil quality sensor 186 may be utilized to determinewhat approach to take (e.g. trapping a high-pressure charge or trappinga negative pressure with respect to atmosphere) to deactivate one ormore engine cylinder(s), as will be discussed in further detail below.

In some examples, engine 10 may further include an in-cylinder pressuresensor 185. In-cylinder pressure sensor may be configured to send datarelated to pressure in the cylinder, to the controller.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed. Example routines are shownwith reference to FIGS. 3A-3B.

In some examples, engine 10 may be included in a hybrid vehicle withmultiple sources of torque available to one or more vehicle wheels 197.In other examples, engine 10 may be included in a conventional vehiclewith only an engine. In the example shown, the vehicle includes engine10 and an electric machine 194. Electric machine 194 may be a motor or amotor/generator. Crankshaft 140 of engine 10 and electric machine 194are connected via a transmission 196 to vehicle wheels 197 when one ormore clutches are engaged. In the depicted example, a first clutch 193is provided between crankshaft 140 and electric machine 194, and asecond clutch 198 is provided between electric machine 194 andtransmission 196. Controller 12 may send a signal to an actuator (notshown) of each clutch (e.g. 193, 198) to engage or disengage theclutch(s), so as to connect or disconnect crankshaft 140 from electricmachine 194 and the components connected thereto, and/or connect ordisconnect electric machine 194 from transmission 196 and the componentsconnected thereto. Transmission 196 may be a gearbox, a planetary gearsystem, or another type of transmission. The powertrain may beconfigured in various manners including as a parallel, a series, or aseries-parallel hybrid vehicle.

Electric machine 194 receives electrical power from a traction battery195 to provide torque to vehicle wheels 197. Electric machine 194 mayalso be operated as a generator to provide electrical power to chargebattery 195, for example during a braking operation.

Thus, a system for a vehicle may comprise a variable displacementengine, including a set of cylinders and where each cylinder is coupledto a fuel injector and a spark plug, and where each cylinder includes apiston. The system may further include a controller, storinginstructions in non-transitory memory that, when executed, cause thecontroller to, in response to conditions being met for deactivating acylinder or a plurality of cylinders from the set of cylinders,determining whether to deactivate the cylinder or the plurality ofcylinders by trapping a vacuum in the cylinder or the plurality ofcylinders, or to deactivate the cylinder or the plurality of cylindersby trapping a high-pressure charge in the cylinder or the plurality ofcylinders. In response to trapping the vacuum in the cylinder or theplurality of cylinders, the controller may provide spark when the pistonor pistons in the cylinder or the plurality of cylinders are within athreshold of bottom dead center, but may not provide fuel to thecylinder or the plurality of cylinders while the cylinder or theplurality of cylinders are deactivated. Alternatively, responsive totrapping the high-pressure charge in the cylinder or the plurality ofcylinders, the controller may discontinue providing both spark and fuelto the cylinder or the plurality of cylinders.

Such a system may further comprise a crankshaft coupled to the variabledisplacement engine, a crankshaft position sensor, a camshaft coupled tothe variable displacement engine, and a camshaft position sensor. Thecontroller may store further instructions to indicate, via one or moreof the crankshaft sensor and/or the camshaft sensor, whether a piston orpistons of the cylinder or the plurality of the cylinders, respectively,are within the threshold of bottom dead center, where the threshold ofbottom dead center comprises a predetermined number of degrees from thebottom dead center position while the cylinder or the plurality ofcylinders are deactivated via trapping the vacuum, and where responsiveto the piston or pistons being within the threshold of bottom deadcenter position, providing spark via the spark plug.

Such a system may further comprise an oil quality sensor. In such anexample, the controller may store further instructions to determine todeactivate the cylinder or the plurality of cylinders by trapping thevacuum in response to an indication that an oil quality is greater thanan oil quality threshold, and to deactivate the cylinder or theplurality of cylinders by trapping the high-pressure charge in responseto an indication that the oil quality is lower than the oil qualitythreshold.

Another example of a system for a vehicle may comprise a variabledisplacement engine, including a set of cylinders and where eachcylinder is coupled to a fuel injector and a spark plug, and where eachcylinder includes a piston, a crankshaft mechanically coupled to thevariable displacement engine, and a crankshaft position sensor. Such asystem may further comprise a controller, storing instructions innon-transitory memory that, when executed, cause the controller todeactivate a first subset of cylinders that includes one or morecylinders from the set of cylinders in response to predeterminedconditions being met, where deactivating the first subset of cylindersincludes at least sealing and stopping providing fuel injection to thefirst subset of cylinders. The controller may store further instructionsto maintain a second subset of cylinders that includes one or morecylinders from the set of cylinders activated to combust air and fuel,and to monitor acceleration of the crankshaft while the first subset ofcylinders is deactivated. In response to acceleration of the crankshaftgreater than a crankshaft acceleration threshold, the controller maystore further instructions to retard a spark provided to an activatedcylinder included in the second subset of cylinders, the activatedcylinder comprising a cylinder scheduled to combust air and fuelimmediately following the acceleration of the crankshaft greater thanthe crankshaft acceleration threshold. The controller may store furtherinstructions to assign the first subset of cylinders to be reactivatedto combust air and fuel and the second subset of cylinders to bedeactivated, immediately following retarding the spark provided to theactivated cylinder.

In such a system, acceleration of the crankshaft greater than thecrankshaft acceleration threshold is a result of an unintendedcombustion in a deactivated cylinder included in the first subset ofcylinders. In such an example, the controller may store furtherinstructions to exhaust residual burnt gas in the deactivated cylinderresulting from the unintended combustion prior to reactivating the firstsubset of cylinders including the deactivated cylinder.

In another example of such a system, the controller may store furtherinstructions to provide spark to the first subset of cylinders while thefirst subset is deactivated, and to provide spark to the second subsetof cylinders while the second subset is deactivated, where providingspark includes providing spark when pistons coupled to cylindersincluded in the first subset and/or the second subset are atpredetermined positions in relation to the crankshaft.

Yet another example of such a system may further comprise an oil qualitysensor. In such an example, the controller may store furtherinstructions to deactivate the first subset and/or the second subset ofcylinders by trapping a negative pressure with respect to atmosphericpressure in the first subset and/or second subset of cylinders inresponse to an indication that an oil quality of an oil utilized forcooling, lubrication and/or cleaning of the variable displacement engineis greater than an oil quality threshold, and to deactivate the firstsubset and/or the second subset of cylinders by trapping a positivepressure with respect to atmospheric pressure in the first subset and/orthe second subset of cylinders in response to an indication that the oilquality is below the oil quality threshold.

Turning now to FIG. 3A, a flowchart for a high-level example method 300is shown for reducing unintended/undesired combustion events andpreventing spark plug fouling in response to deactivation of one or moreengine cylinders. Method 300 will be described in reference to thesystems described in FIGS. 1-2, though it should be understood thatmethod 300 may be applied to other systems without departing from thescope of this disclosure. Method 300 may be carried out by a controller,such as controller 12, and may be stored as executable instructions innon-transitory memory. Instructions for carrying out method 300 and therest of the methods included herein may be executed by the controllerbased on instructions stored on a memory of the controller and inconjunction with signals received from sensors of the vehicle system,such as the sensors described above with reference to FIGS. 1-2. Thecontroller may employ engine system actuators such as spark plug(s)(e.g. 192), fuel injector(s) (e.g. 166), etc., according to the methodsdepicted below.

Method 300 begins at 302, and may include estimating and/or measuringengine operating conditions. These may include, for example, enginespeed, desired torque (for example, from a pedal-position sensor),manifold pressure (MAP), manifold air flow (MAF), BP, enginetemperature, catalyst temperature, intake temperature, spark timing, airtemperature, knock limits, etc.

Proceeding to 304, method 300 may include determining, based on theestimated operating conditions, an engine mode of operation (e.g., VDEor non-VDE). For example, if the torque demand is low, the controllermay determine that one or more cylinders can be deactivated while thetorque demand is met by the remaining active cylinders. In comparison,if the torque demand is high, the controller may determine that all thecylinders need to remain active.

Proceeding to 306, method 300 may include confirming whether VDE modeconditions (e.g. cylinder deactivation conditions) are met. In oneexample, cylinder deactivation conditions may be confirmed when torquedemand is less than a threshold. If cylinder deactivation conditions areconfirmed, a VDE mode is selected. If cylinder deactivation conditionsare not confirmed, at 310, the routine includes maintaining all thecylinders active and combusting.

If cylinder deactivation conditions and a VDE mode of operation areconfirmed, then method 300 may proceed to 312. At 312, method 300 mayinclude determining a quality of oil included in the engine forlubrication, cleaning, and cooling of various engine components. In oneexample, the oil is engine oil, or motor oil. Determining a quality ofoil at 312 may include determining whether the quality of the oil isabove an oil quality threshold, or below the oil quality threshold,where oil quality above the threshold indicates higher (e.g. better)quality oil, and where oil quality below the threshold indicates lower(e.g. lesser) quality oil. Higher, or better, quality oil may compriseoil which is more effective at lubricating, cleaning, and/or drawingheat from the engine, whereas lower quality, or lesser quality oil maycomprise oil which is less effective at lubricating, cleaning, and/ordrawing heat from the engine. In one example, oil quality above thethreshold may include oil which, if spark is continued to be provided toa deactivated cylinder during a VDE event, may prevent fouling of thespark plug. In other words, migration of oil into the deactivated enginecylinder (with vacuum trapped in the cylinder) may not foul the sparkplug, as long as spark is provided (near BDC) while the cylinder isdeactivated. Alternatively, oil quality below the threshold may compriseoil quality where, if migration of oil were to occur while a cylinder isdeactivated (with vacuum in the cylinder), even if spark is providedduring the deactivation, the spark plug may still be susceptible tofouling.

In some examples, the oil quality threshold may be adjusted as afunction of vehicle operating conditions, such as vehicle speed, enginespeed, engine load, engine temperature, oil temperature, etc. Forexample, depending on the various vehicle operation conditions, it maybe indicated how susceptible to oil migration a deactivated cylinder maybe, under situations where vacuum is trapped in the cylinder upondeactivation. For example, lower engine speeds, lower vehicle speeds,lower engine loads, etc., may result in less oil migration to adeactivated cylinder with trapped vacuum, than higher engine speeds,higher vehicle speeds, higher engine loads, etc. Thus, the oil qualitythreshold may be adjusted as a function of how susceptible to oilmigration one or more deactivated cylinders may be, where suchsusceptibility is based on the above-mentioned vehicle operatingparameters. As one example, consider a situation where oil quality islow, but where vehicle operating conditions are such that oil migrationinto a deactivated cylinder (with trapped vacuum) is less likely. Suchconditions may include lower engine speeds, lower engine loads, etc. Insuch an example, the threshold may be adjusted such that the thresholdis lowered. In another example, the threshold may be raised, responsiveto vehicle operating conditions being such that oil migration into adeactivated cylinder (with trapped vacuum) is more likely.

Accordingly, at 312, if oil quality is indicated to be below thethreshold, method 300 may proceed to FIG. 3B, where deactivation of theone or more engine cylinder(s) may be conducted such that a high-energycharge is trapped in the cylinder(s), which may reduce the potential forspark plug fouling, by reducing/preventing oil migration into thecylinder(s). However, a disadvantage to such a method may be a torquebump present at deactivation. Thus, when possible, it may be desirableto deactivate the cylinder(s) by trapping a vacuum rather than ahigh-pressure charge. In any event, a method for trapping thehigh-pressure charge at deactivation will be discussed in detail belowat FIG. 3B.

Alternatively, at 312, in response to an indication that oil quality isgreater than the oil quality threshold, method 300 may proceed to 314.At 314, method 300 may include selecting one or more engine cylinders todeactivate based on the estimated engine operating conditions. In someexamples, a group of cylinders or a bank of cylinders may bedeactivated. The selection may be based on, for example, which cylinderor cylinders were deactivated during a previous VDE mode of operation.For example, if during the previous cylinder deactivation condition, afirst cylinder or first group of cylinders on a first engine bank weredeactivated, then a controller may select a second cylinder or a secondgroup of cylinders on a second engine bank for deactivation during thepresent VDE mode of operation. As another example, the selection may bebased on a regeneration state of a first exhaust catalyst (or emissioncontrol device) coupled to the first bank relative to the regenerationstate of a second exhaust catalyst (or emission control device) coupledto the second bank.

Following the selection, also at 314, the controller may selectivelydeactivate the one or more engine cylinders. As used herein, thedeactivation may include selectively deactivating (e.g., turning off) afuel injector of the selected one or more engine cylinders. Morespecifically, as discussed above, deactivation of one or more enginecylinders as discussed herein may include the controller commanding theselected one or more cylinders to be deactivated just after an exhauststroke has been conducted. In other words, just after the piston(s)corresponding to the one or more selected cylinder(s) to be deactivatedhave pushed combustion gases out of the exhaust valve to the exhaustsystem, the exhaust valve(s) may be commanded closed via the controller(e.g. 12). Furthermore, the intake valve(s) corresponding to the one ormore selected cylinder(s) may be commanded/maintained closed via thecontroller. In this way, rather than trapping a high-pressure charge inthe cylinder (see FIG. 3B), a vacuum (negative pressure with respect toatmospheric pressure) may be trapped in the one or more selectedcylinder(s). As discussed, trapping the vacuum in the one or moreselected cylinder(s) may reduce or eliminate torque bump(s) atdeactivation, but may lead to increased oil consumption, spark plugfouling, and/or undesired combustion events if mitigating action is notundertaken.

Accordingly, proceeding to 316, method 300 may include commanding sparkto each of the one or more deactivated engine cylinder(s) near BDC. Inone example, “near” BDC may comprise within 5 degrees or less of BDC. Inanother example, “near” BDC may comprise within 10 degrees or less ofBDC. In yet another example, “near” BDC may comprise within 20 degreesor less of BDC. In other words, spark may be provided to each of the oneor more deactivated engine cylinders within a predetermined threshold(e.g. predetermined number of degrees of) of BDC.

To determine whether a deactivated engine cylinder piston is near BDC(e.g. within a threshold of BDC), a crankshaft position sensor (e.g.120) and/or one or more camshaft sensor(s) (e.g. 188, 189) may beutilized.

In one example, spark may be provided near BDC (e.g. within thethreshold of BDC) at every occasion that the piston(s) corresponding tothe deactivated cylinder(s) are near BDC. More specifically, each enginecycle (intake, compression, power, and exhaust stroke) may include twooccasions that the piston(s) corresponding to the deactivatedcylinder(s) are near BDC. Thus, in one example, each time the piston(s)are near BDC, spark may be provided.

In an example where spark is provided every occasion the piston(s) arewithin the threshold of BDC, ignition energy of the spark may becontrolled via the controller. For example, because spark is provided ateach occasion the piston(s) are near BDC, ignition energy may be keptrelatively low. In other words, the frequency of sparking (e.g. everyBDC occasion) may prevent any oil that may migrate into the deactivatedcylinder(s) from fouling the spark plug(s), without a need forincreasing ignition energy.

Discussed, herein, increasing the ignition energy of the spark deliveredto the cylinder(s) may include increasing an ignition coil dwell timing.As an example, ignition coil dwell timing may be increased bymaintaining a voltage applied to the ignition coil of the spark plug ata substantially constant value for a longer duration than a typicalignition coil dwell time. The longer dwell time may increase a primarycurrent that the coil charges to, thus increasing its stored inductiveenergy. As one example, the typical ignition coil dwell time maycomprise 2.5 msec, and increasing the dwell time may comprise increasingthe ignition coil dwell time to 2.8 msec, which may thus increase thepeak primary current from 8 amps to 10 amps.

Increasing the ignition energy may additionally or alternatively includeincreasing a number of strikes of the ignition coil for each sparkevent. Herein, the higher strike frequency is used to increase a numberof sparks output by the ignition coil per spark event for the determinednumber of BDC events following the cylinder deactivation. In oneexample, the strike frequency may be increased from one strike per sparkevent to five strikes per spark event.

Discussed herein, ignition energy that is not “increased” may bereferred to as “basal” ignition energy. Basal ignition energy maycomprise ignition coil dwell time of 2.5 msec, and/or a strike frequencyof one strike per spark event. Thus, increasing, or increased ignitionenergy may comprise ignition energy increased as compared to the basalignition energy.

In another example, spark may be provided at each occasion of BDC,except for the first occasion of BDC after deactivation. Morespecifically, each time that spark is provided, electrical energy may beutilized, which may decrease a state of charge (SOC) of an onboard powersupply (e.g. battery 195). Thus, in a hybrid vehicle, it may bedesirable to use electrical energy as efficiently as possible.Accordingly, in one example, spark may not be provided at the firstoccasion of BDC after deactivation, but may be provided at everyoccasion of BDC thereafter. In such an example, the spark provided maycomprise the basal ignition energy. In other words, ignition energy maybe kept low, as the spark is provided at every occasion of BDC after thefirst occasion after deactivation. By providing the basal ignitionenergy spark at every occasion of BDC, any oil that may migrate to thedeactivated cylinder(s) may be prevented from fouling the spark plug(s),without increasing ignition energy.

In another example, spark may be provided at every other occasion of BDCafter deactivation. In other words, spark may be provided once perengine cycle. In such an example, spark may not be provided at the firstBDC occasion after deactivation, but may be provided at the second BDCoccasion, and every other BDC occasion thereafter. In one example,ignition energy may be kept at the basal ignition energy for apredetermined number of spark events (e.g. every other BDC occasion),but may then be increased. In one example the predetermined number ofspark events that the ignition energy is kept low for may comprise twospark events, three spark events, 5-10 spark events, 10-20 spark events,etc. In one example, the predetermined number of spark events maycomprise a number of spark events where substantial oil migration intothe cylinder(s) is not yet expected, such that sparking at the basalignition energy may be sufficient to prevent spark plug fouling.However, after the predetermined number of spark events has elapsed,ignition energy may be increased, as the more time spent in thedeactivated state with vacuum trapped in the deactivated cylinder, themore likely that substantial oil migration into the deactivated cylindermay occur. Thus, in such an example, ignition energy may be increasedfor a remaining duration of the deactivation.

In another example, the spark provided near BDC subsequent todeactivation of one or more engine cylinder(s) may be a function ofvehicle speed. For example, a frequency of spark events near BDC may beincreased proportional to an increase in vehicle speed, and decreasedproportionally to a decrease in vehicle speed. Consider an example wherethe vehicle is traveling at a higher speed (e.g. 40 mph or greater).Upon deactivation of one or more engine cylinder(s), the rapid speed ofthe engine may make the engine more prone to oil migration, as comparedto when the cylinder(s) are deactivated at lower speeds (e.g. less than40 mph). Such an example is meant to be illustrative, and is not meantto be limiting in any way. In other words, there may be a thresholdvehicle speed (e.g. 40 mph), where if one or more cylinder(s) aredeactivated and vehicle speed is above the threshold speed, thenfrequency of spark events may be increased, as compared to the frequencyof spark events if the vehicle speed is below the threshold speed. Inone example, if the vehicle speed is above the threshold speed atdeactivation, spark may be provided near BDC at every BDC occasion afterdeactivation. Alternatively, if the vehicle speed is below the thresholdspeed at deactivation, spark may be provided near BDC at every other BDCoccasion after deactivation.

In some examples, frequency of spark provided and/or an ignition energyof spark provided near BDC may be a function of pressure inside thecylinder at deactivation. For example, as pressure in a deactivatedcylinder or cylinders becomes more negative with respect to atmosphericpressure, oil migration may be more likely, thus a frequency of sparkprovided may be increased, and/or ignition energy may be increased. Inone example, pressure in deactivated cylinder(s) may be monitored via anin-cylinder pressure sensor (e.g. 185). As one example, at deactivation,pressure in the cylinder(s) may be monitored, and spark may be providedresponsive to pressure in the cylinder(s) reaching a predeterminednegative pressure or vacuum, with respect to atmospheric pressure. Sparkmay initially be provided at the basal ignition energy, for example.However, while the cylinder is deactivated, in response to pressurereaching a second negative pressure threshold that is more negative thanthe first threshold, spark frequency and/or ignition energy may beincreased, to reduce oil migration to the deactivated cylinder(s). Insome examples, rather than relying on an in-cylinder pressure sensor,other methodology may be utilized to infer in-cylinder pressure.Examples may include time spent in a deactivated state, etc.

In another example where the spark provided near BDC is a function ofvehicle speed, the spark provided may comprise increased ignition energyover basal ignition energy if vehicle speed is above the threshold, andlowered (e.g. basal) ignition energy if vehicle speed is below thethreshold. For example, if vehicle speed is above the threshold, thenthe spark provided may comprise the increased ignition energy, withoutany spark comprising the basal ignition energy. In such an example,spark may be provided at each BDC occasion, or every other BDC occasion.In an example where vehicle speed is below the threshold, then the sparkprovided may comprise the basal ignition energy. In such an example, thebasal ignition energy may be provided at each BDC occasion afterdeactivation, or every other BDC occasion. Furthermore, the basalignition energy may be provided for a predetermined number of sparkevents, similar to that discussed above, and then may be increasedsubsequent to the predetermined number of spark events elapsing.

It may be understood that the above examples are meant to beillustrative, and that there may be circumstances where frequency ofspark events near BDC for a deactivated engine cylinder may be adjusted.For example, it is within the scope of this disclosure to, for example,delay sparking near BDC after deactivation for a predetermined number ofBDC occasions (e.g. 1, 2, 3, 4, 5, greater than 5 but less than 10,greater than 10 but less than 20, greater than 20 but less than 30,etc.), and then start sparking near BDC. In such an example, when thesparking is commenced, the sparking may be every other BDC occasion,every other BDC occasion, every third BDC occasion, every fourth BDCoccasion, etc. In such an example, ignition energy may comprise thebasal ignition energy, or may comprise increased ignition energy. In oneexample, basal ignition energy may be conducted for each spark event fora predetermined number of spark events, and after the predeterminednumber of spark events has elapsed, then subsequent spark events maycomprise increased ignition energy spark events.

In another example, spark frequency and/or ignition energy provided ateach spark event may be a function of oil temperature. For example, athigher oil temperatures, oil migration may be expected to migrate morereadily into a deactivated engine cylinder (with trapped vacuum), thanat lower oil temperatures. Thus, in response to an indicated oiltemperature greater than a threshold, where the threshold comprises anoil temperature where migration of oil into deactivated cylinder(s) isexpected to be greater than if engine oil temperature is below thethreshold, spark frequency and/or ignition energy provided at each sparkevent, may be increased, as compared to conditions where engine oiltemperature is below the threshold. As discussed above, frequency and/orignition energy provided may additionally be adjusted as a function ofvehicle operating conditions, such as vehicle speed, for example.

The engine may continue to be operated in the VDE mode with one or moreengine cylinders deactivated until reactivation conditions are met atstep 318 of method 300. In one example, reactivation conditions may bemet when engine torque demand increases above a threshold. In anotherexample, reactivation conditions may be considered met when the enginehas operated in the VDE mode for a specified duration. Accordingly, at318, non-VDE conditions may be confirmed. If non-VDE conditions are notconfirmed, the engine may continue to be operated in the VDE mode at 320with the selected deactivated one or more cylinders sealed (e.g. intakeand exhaust valve(s) closed, with fueling to the deactivated cylinder(s)stopped, and with spark being provided to the one or more deactivatedcylinders near BDC occasions.

Upon confirming non-VDE conditions, at 318, the deactivated cylinder(s)may be reactivated. Specifically, the deactivated fuel injector(s) maybe reactivated, and spark may be provided to the deactivated enginecylinder(s). Reactivation of the deactivated engine cylinder(s) maycomprise commanding spark to the reactivated cylinder near TDC (e.g.just prior or within a threshold number of degrees of TDC).

In this way, spark plug fouling may be prevented under situations wheredeactivation of one or more engine cylinder(s) comprises trapping avacuum in the one or more engine cylinder(s). Such a method may bedesirable over a method where a high-pressure charge is trapped in thecylinder(s), because when vacuum is trapped in the cylinder(s), a torquebump may be reduced or eliminated in response to deactivation and/orreactivation. However, as discussed above, there may be conditions whereoil quality is such that it may be desirable to trap the high-pressurecharge in the deactivated cylinder(s), in order to reduce/prevent oilmigration into the cylinder(s), to prevent/reduce opportunities forspark plug fouling, to reduce oil consumption, etc.

Accordingly, returning to step 312 of method 300, if oil quality isindicated to be below the threshold, method 300 may proceed to FIG. 3B.

FIG. 3B depicts a method 350, which may comprise a sub-method of method300 depicted at FIG. 3A. Method 350 begins at 355, and may includedetermining which cylinder(s) to deactivate. Selection of whichcylinder(s) to deactivate may be conducted as previously discussed atstep 314 of method 300, and thus will not be reiterated here forbrevity.

Responsive to determining which cylinder(s) are to be deactivated,method 350 may proceed to 360. At 360, method 350 may includedeactivating the cylinder(s) by trapping a high-pressure charge in thecylinder(s) selected for deactivation. More specifically, to trap thehigh-pressure charge in the cylinder(s), the following methodology maybe utilized. For the particular cylinder(s), the cylinder(s) may intakeair during the intake stroke, and fueling and spark may be providedduring the compression stroke (or in some examples fueling may beprovided during the intake stroke) to combust air and fuel. However,rather than exhausting the combusted gases, the high-pressure charge maybe trapped inside the cylinder(s) by the controllercommanding/maintaining closed both the intake and exhaust valvescorresponding to the particular cylinder(s) selected for deactivation.By preventing the combusted gases from being routed to the exhaustsystem, the high-pressure charge (e.g. combusted air and fuel) may betrapped in the cylinder(s). While discussed is the trapping of thehigh-pressure charge, it may be understood that in some examples, airmay be inducted into a cylinder scheduled for deactivation, and then thecylinder may be sealed without combustion (no fueling or spark), thustrapping a positive pressure with respect to atmospheric pressure in theparticular cylinder. In some examples, trapping the positive pressureinstead of the high-pressure charge may comprise an indication that theoil quality is below the threshold, but greater than a second oilquality threshold, for example. While such action is within the scope ofthis disclosure, the description with regard to FIG. 3B centers ontrapping the high-pressure charge.

It may be understood that, with the high-pressure charge trapped in thecylinder(s), spark may not be provided while the cylinder isdeactivated, and fueling to the cylinder(s) is shut off.

In response to the high-pressure charge being trapped in thecylinder(s), method 350 may proceed to 365. Steps 365 to 375 areessentially equivalent to steps 318 to 322 of method 300, and thus willnot be reiterated for brevity. Briefly, the cylinder(s) may remaindeactivated with the trapped high-pressure charge, until non-VDEconditions are met, at which point the cylinder(s) may be reactivated tocombust air and fuel. However, in some examples, even with ahigh-pressure charge (or positive pressure due to inducting air but notcombusting prior to sealing the cylinder) trapped in the cylinder, aftersome time the cylinder may be susceptible to unintended combustion.Thus, in some examples, pressure in the deactivated cylinder may bemonitored (e.g. via in-cylinder pressure sensor 185), and if pressuredrops below a threshold, then spark may be provided near BDC in order toreduce or avoid any potential spark plug fouling. If in-cylinderpressure sensor(s) are not included in the vehicle, or are notfunctioning as desired, in some examples spark may be provided near BDCto a cylinder deactivated by trapping the high-pressure charge orpositive pressure after a predetermined number of engine cycles, orafter a predetermined time duration elapses, etc.

Turning now to FIG. 4, an example map 400 for providing spark andfueling to an engine cylinder, is shown. In example map 400, a singleengine cylinder is shown, for clarity. Furthermore, map 400 illustratesthe deactivation of the engine cylinder. More specifically, map 400includes four engine cycles (engine cycle 1-4), and illustrates thestrokes (exhaust, intake, compression, and power) for each engine cycle.For each engine cycle, engine position is illustrated, showing where topdead center (TDC) and bottom dead center (BDC) are in relation to eachengine cycle. Map 400 includes plot 405, indicating valve timing. Line406 illustrates exhaust valve timing, where line 407 illustrates intakevalve timing. Map 400 further includes plot 410, indicating pistonposition in relation to the four engine cycles. Map 400 further includesplot 415, indicating spark ignition energy, in relation to the fourengine cycles. Spark ignition energy may be increased (+) or decreased(−). Map 400 further includes plot 420, indicating whether fuelinjection to the engine cylinder is on, or off, in relation to the fourengine cycles.

Referring to engine cycle 1, the exhaust valve first opens and closes(line 406) during the exhaust stroke, and then the intake valve opensand closes (line 407) during the intake stroke. Spark and fueling areprovided to the engine cylinder during the compression stroke. In thisexample map 400, spark ignition energy may be understood to comprisebasal spark ignition energy.

Engine cycle 2 depicts the same process as engine cycle 1. In otherwords, engine cycle 1 and engine cycle 2 illustrate conditions where thecylinder is not deactivated, thus the intake and exhaust valves areopening and closing, and fuel injection and spark are being provided tothe engine. In other words, engine cycle 1 and engine cycle 2 depictengine cycles where conditions are not met for operating the engine inVDE mode.

Engine cycle 3 illustrates the exhaust valve opening, and then closing.It may be understood that at engine cycle 3, conditions are met foroperating the engine in VDE mode. For clarity, the engine cylinderdepicted at map 400 comprises the cylinder selected for deactivation(although there may be other cylinders additionally selected, dependingof vehicle operating conditions). Accordingly, after the exhaust stroke,where the exhaust stroke includes the exhaust valve opening, and thenclosing, the intake valve is commanded closed/maintained closed via thecontroller, and fuel injection is stopped (e.g. fuel injection is off).By closing the exhaust valve (and maintaining the intake valve closed,without fuel injection) after exhaust gases are pushed out of thecylinder, a vacuum may develop in the deactivated cylinder. Such avacuum may result in oil migration into the cylinder, as discussedabove. Thus, to prevent fouling of the spark plug while the cylinder isdeactivated, spark may be provided at BDC, discussed above, and whichwill be further discussed below.

At engine cycle 3, the piston is at BDC just after the intake strokesubsequent to deactivation, however in this example map 400, spark isnot provided at the first BDC occasion. Rather, spark is provided at thesecond BDC occasion (just after the power stroke in engine cycle 3). Asdiscussed above, providing spark at BDC may comprise providing spark“near” BDC, which may include providing spark within a predeterminedthreshold (predetermined crank angle degrees) of BDC. Referring toengine cycle 4, spark is provided at every BDC occasion after the secondBDC occasion. In example map 400, it may be understood that the ignitionenergy provided at each spark event comprises the basal ignition energy.

In other words, example map 400 depicts a situation where spark isdelayed (for one BDC occasion after deactivation), but where spark isprovided at every BDC occasion subsequent to the first BDC occasion.Because spark is provided at every BDC occasion subsequent to the firstBDC occasion, spark ignition energy comprises the basal ignition energy,as due to the frequency of sparking (e.g. every BDC occasion after thefirst BDC occasion), it may be expected that spark plug fouling may beavoided.

Example map 400 only illustrates four engine cycles, but it may beunderstood that deactivation of the engine cylinder illustrated at FIG.4 may be conducted for any number of engine cycles. Thus, it may beunderstood that subsequent to engine cycle 4, spark may continue to beprovided at every BDC occasion, where the spark provided comprises thebasal ignition energy. In response to conditions being met forreactivating the deactivated cylinder, it may be understood that thefuel injectors may be reactivated to provide fueling to the cylinder,and spark may be provided near TDC (e.g. just prior to or within athreshold of TDC).

Turning now to FIG. 5, an example map 500 for providing spark to adeactivated engine cylinder, is shown. Similar to that discussed abovefor FIG. 4, FIG. 5 illustrates a single engine cylinder, for clarity.Map 500 includes four engine cycles (engine cycle 1-4), and illustratesthe strokes (exhaust, intake, compression, and power) for each enginecycle. For each engine cycle, engine position is illustrated, showingwhere TDC and BDC are in relation to each engine cycle. Map 500 includesplot 505, indicating valve timing. Line 506 illustrates exhaust valvetiming. Map 500 further includes plot 510, indicating piston position inrelation to the four engine cycles. Map 500 further includes plot 515,indicating spark ignition energy, in relation to the four engine cycles.Map 500 further includes plot 520, indicating whether fuel injection tothe engine cylinder is on, or off, in relation to the four enginecycles. Example map 500 depicts a situation where VDE conditions areindicated to be met, and the cylinder selected for deactivationcomprises the cylinder illustrated at map 500. Thus the cylinder isdeactivated at engine cycle 1, as will be discussed in further detailbelow.

Referring to engine cycle 1, it may be understood that VDE conditionsare met, thus the exhaust valve first opens and closes (line 506) duringthe exhaust stroke. As the cylinder is selected for deactivation, theintake valve is maintained closed at engine cycle 1. As discussed above,by opening the exhaust valve and then closing it, to deactivate thecylinder, a vacuum may be trapped in the cylinder, which may encouragemigration of oil into the cylinder, if mitigating actions are notundertaken. Thus, to prevent fouling of the spark plug corresponding tothe deactivated cylinder as a result of the oil migration, spark may beprovided near BDC. In this example map 500, it may be understood that itillustrates a situation where spark is provided at every other BDCoccasion, and where the first two BDC occasions include providing sparkat the basal ignition energy, whereas subsequent BDC occasions includeproviding spark at increased ignition energy (as compared to the basalignition energy).

Thus, referring to engine cycle 1, subsequent to deactivation of thecylinder, where fuel is shut off to the engine cylinder (plot 520),spark is not provided at the first BDC occasion, but spark is providedat the second BDC occasion. Similarly, referring to engine cycle 2, 3,and 4, spark is provided once per engine cycle. By providing spark nearBDC, it may be understood that no combustion is expected, due to thelarge cylinder volume when the piston is near BDC. In other words, evenif a combustion event were to happen when the piston is near BDC, notorque may be produced. By providing spark once per engine cycle, ratherthan at each BDC occasion, spark plug fouling may be reduced orprevented, and battery power may be reduced, as compared to providingspark at every BDC occasion. Thus, such a method of providing sparkevery other BDC occasion may be a function of a SOC of the battery, inone example. For instance, if battery charge is below a threshold, thenit may be desirable to provide spark in a fashion where spark isprovided every other BDC occasion, or once per engine cycle.

After the first two spark events at the basal ignition energy (enginecycle 1 and engine cycle 2), subsequent spark events (engine cycle 3 andengine cycle 4) are illustrated to comprise increased ignition energy ascompared to the basal ignition energy. In other words, because the sparkis only provided once per engine cycle, as the deactivation time (andnumber of engine cycles) increases, the opportunity for oil migration(and thus spark plug fouling), increases. Thus, after a predeterminednumber of spark events (two in this example map 500) at the basalignition energy, spark energy may be increased, to ensure that sparkfouling does not occur. It may be understood that providing increasedignition energy may comprise utilizing more energy stored in thebattery, thus the amount of increased ignition energy may be a functionof battery SOC. For example, the ignition energy for each spark event(post-basal ignition energy spark events) may be controlled via thecontroller so as to maintain a desired battery SOC for a subsequentapplication. In other words, ignition energy may be controlled so as tomaintain a threshold battery SOC. The threshold SOC may comprise abattery SOC where subsequent applications that use battery power are notadversely affected.

Example map 500 only illustrates four engine cycles, but it may beunderstood that deactivation of the engine cylinder illustrated at FIG.5 may be conducted for any number of engine cycles. Thus, it may beunderstood that subsequent to engine cycle 4, spark may continue to beprovided at every other BDC occasion, where the spark provided comprisesthe increased ignition energy. In response to conditions being met forreactivating the deactivated cylinder, it may be understood that thefuel injectors may be reactivated to provide fueling to the cylinder,and spark may be provided near TDC (e.g. just prior or within athreshold of TDC).

Turning now to FIG. 6, another example map 600 for providing spark to adeactivated engine cylinder, is shown. Similar to that discussed aboveat FIG. 4 and FIG. 5, a single engine cylinder is illustrated, forclarity. Map 600 includes a number of engine cycles, including enginecycle 1, engine cycle 2, engine cycle “n” (which may occur some durationof time after engine cycle 2), and engine cycle “n+1”, which may occurjust after engine cycle “n”. For each engine cycle shown, the strokes(exhaust, intake, compression, and power) are shown. For each enginecycle, engine position is illustrated, showing where TDC and BDC are inrelation to each engine cycle. Map 600 includes plot 605, indicatingvalve timing. Line 606 illustrates exhaust valve timing. Map 600 furtherincludes plot 610, indicating piston position in relation to the enginecycles. Map 600 further includes plot 615, indicating spark ignitionenergy, in relation to the engine cycles. Map 600 further includes plot620, indicating whether fuel injection to the engine cylinder is on, oroff, in relation to the engine cycles. Example map 600 depicts asituation where VDE conditions are indicated to be met, and the cylinderselected for deactivation comprises the cylinder illustrated at map 600.Thus, the cylinder is deactivated at engine cycle 1, as will bediscussed in further detail below.

Referring to engine cycle 1, it may be understood that VDE conditionsare met, thus the exhaust valve first opens and closes (line 606) duringthe exhaust stroke. As the cylinder is selected for deactivation, theintake valve is maintained closed at engine cycle 1. As discussed above,by opening the exhaust valve and then closing it, to deactivate thecylinder, a vacuum may be trapped in the cylinder, which may encouragemigration of oil into the cylinder, if mitigating actions are notundertaken. Thus, to prevent fouling of the spark plug corresponding tothe deactivated cylinder as a result of the oil migration, spark may beprovided near BDC (e.g. within a threshold of BDC). In this example map600, it may be understood that it illustrates a situation where spark isprovided at every BDC occasion, and where the spark provided comprisesthe basal ignition energy for a predetermined number of engine cycles(or predetermined duration in some examples), and then transitions to anincreased ignition energy after the predetermined number of enginecycles, or predetermined duration of time, elapses.

Thus, referring to engine cycle 1, subsequent to deactivation of thecylinder, where fuel is shut off to the engine cylinder (plot 620),spark is provided at the first BDC occasion, and every BDC occasionthereafter (see engine cycles 2, n, and n+1). In other words, spark isprovided twice per engine cycle. Initially, the spark provided comprisesthe basal ignition energy, indicated at engine cycle 1 and engine cycle2. The spark comprising the basal ignition energy is provided for apredetermined number of engine cycles. The predetermined number ofengine cycles may comprise a number of engine cycles where it may beexpected that providing the basal ignition energy may be sufficient toprevent fouling of the spark plug. In some examples, the predeterminednumber of engine cycles may be a function of engine load, vehicle speed,engine speed, oil temperature, etc. In other words, the number ofpredetermined engine cycles for which the basal ignition energy isprovided may be variable as a function of vehicle operating conditions.

Subsequent to the predetermined number of engine cycles where the basalignition energy is provided elapsing, the ignition energy may beincreased for any subsequent engine cycles. Similarly to the enginecycles where the basal ignition energy is provided at each BDC occasion,after increasing the ignition energy, the increased ignition energy maybe provided at each subsequent BDC occasion. Alternatively, in someexamples after increasing the ignition energy, spark may only beprovided every other BDC occasion. Depicted at map 600, engine cycle ncorresponds to the first engine cycle where the spark ignition energyhas been increased, and engine cycle n+1 corresponds to the secondengine cycle after spark ignition energy has been increased.

As discussed above, by providing spark at BDC, it may be understood thatno combustion is expected, due to the large cylinder volume when thepiston is at BDC. Furthermore, even if a combustion event were to happenat BDC, because the piston is at BDC, no torque may be produced. Byproviding spark twice per engine cycle, spark plug fouling may bereduced or prevented. In some examples, such a method of providing sparkat every BDC occasion may be a function of a SOC of the battery. Forinstance, if battery charge is above a threshold, then it may bedesirable to provide spark in a fashion where spark is provided everyBDC occasion, or twice per engine cycle. The threshold battery chargemay comprise an amount of charge where, providing spark at every BDCoccasion may not deplete the battery to a level where it may adverselyaffect any subsequent vehicle operating conditions which may utilizepower from the battery.

Turning now to FIG. 7, another example map 700 is shown. Specifically,map 700 illustrates a situation where, for a particular drive cycle withtwo VDE events, one of the VDE events is conducted via trapping vacuumin a cylinder or cylinders selected for deactivation, whereas the otherVDE event is conducted via trapping a high-pressure charge in thecylinder or cylinders selected for deactivation. Similar to thatdiscussed above at FIGS. 4-6, a single engine cylinder is depicted atFIG. 7, for clarity. Map 700 includes a number of engine cycles,depicted as E, I, C, and P, corresponding to exhaust, intake,compression, and power strokes, respectively. Furthermore, similar toFIGS. 4-6, map 700 illustrates engine position, showing where TDC (T)and BDC (B) are in relation to each engine cycle. Map 700 includes plot705, indicating valve timing. For example map 700, it may be understoodthat a valve shown opening and closing during the exhaust stroke (E)corresponds to an exhaust valve for the cylinder, and a valve shownopening and closing during the intake stroke (I) corresponds to anintake valve for the cylinder. Map 700 further includes plot 710,indicating piston position in relation to the engine cycles. Map 700further includes plot 715, indicating spark ignition energy, in relationto the engine cycles. Map 700 further includes plot 720, indicatingwhether fuel injection to the engine cylinder is on, or off, in relationto the engine cycles. Map 700 further includes plot 725, indicating aquality of oil (e.g. engine oil, or motor oil) that is used tolubricate, clean and/or draw heat from, the engine. Line 726 representsa threshold oil quality where, above the threshold a VDE event maycomprise deactivating the cylinder to trap vacuum, whereas if oilquality is below the threshold oil quality, then responsive to a VDEevent, the cylinder may trap a high-pressure charge.

It may be understood that map 700 depicts a single drive cycle, thesingle drive cycle divided up into five segments, which will beelaborated upon below.

Segment 1 illustrates a portion of the drive cycle where VDE conditionsare met, and oil quality is above the threshold oil quality.Furthermore, it may be understood that the cylinder illustrated at map700 comprises a cylinder selected for deactivation. Accordingly, withoil quality above the threshold, the exhaust valve opens and thencloses, to deactivate the cylinder. In other words, it may be understoodthat the exhaust valve opens to route combusted gases out of thecylinder, and then the exhaust valve closes, thus trapping a vacuum inthe cylinder. As discussed above, trapping vacuum inside the cylindermay result in oil migration to the cylinder, which may result in foulingof the spark plug. Thus, to mitigate such an issue, as illustrated atmap 700, spark is provided at every other BDC occasion while thecylinder is deactivated. It may be understood in example map 700 thatthe spark provided comprises the basal spark ignition energy. Bycontinuing to spark near BDC while fueling is cut off from thedeactivated cylinder, and with the vacuum trapped in the sealed cylinder(intake and exhaust valves closed), fouling of the spark plug may beprevented or reduced during segment 1 of the drive cycle.

At the end of segment 1, while not specifically illustrated, it may beunderstood that conditions are met for reactivating the engine cylinder.As discussed above, such conditions may include a torque demand thatcannot be met with the cylinder (or cylinders) deactivated. Accordingly,segment 2 depicts a portion of the drive cycle where the exhaust valveand intake valve resume operation, and fueling and spark are provided.Importantly, spark is provided just in advance of TDC when the cylinderis reactivated, as opposed to near BDC when the cylinder is deactivated.

Operation of the engine proceeds for a duration of time, illustrated assegment 3, with the cylinder combusting air and fuel. While notexplicitly illustrated, it may be understood that other cylinder(s) ofthe engine may be deactivated during segment 3, but for the cylindershown, it may be understood that the cylinder continues to combust airand fuel throughout the duration of segment 3.

Segment 4 illustrates a segment of the drive cycle where the enginecylinder is combusting air and fuel. At the end of segment 4, it may beunderstood that conditions are met for deactivating the illustratedcylinder. However, oil quality has degraded to below the oil qualitythreshold (plot 725). Accordingly, rather than trapping a vacuum in thecylinder, it may be desirable to trap a high-pressure charge to preventoil migration to the deactivated cylinder. Accordingly, it may beunderstood that at the beginning of segment 5, the cylinder isdeactivated, which includes the cylinder taking in intake air, providingfuel and spark to the cylinder, but where the exhaust valve is notopened (and the intake valve is maintained closed), after the finalcombustion event (fueling and spark provided) prior to deactivation.After the cylinder is deactivated with the trapped high-pressure charge,spark is not provided to the cylinder, and fueling is cut off. In thisway, when oil quality is below the threshold oil quality, oil may beprevented from migrating to the deactivated cylinder during a VDE event.

While not explicitly illustrated, it may be understood that aftersegment 5, the engine may be reactivated, to complete the drive cycle,etc.

Thus, the methods depicted at FIGS. 3A-3B may enable a method comprisingin a first operating condition of a vehicle propelled by a variabledisplacement engine, including an indication that an oil quality of anoil utilized for cooling, lubrication and/or cleaning of the variabledisplacement engine is greater than an oil quality threshold, operatingthe vehicle in a first mode that includes selectively deactivating acylinder of the variable displacement engine by trapping a vacuum in thecylinder. Such a method may further include, in a second operatingcondition of the vehicle, including an indication that the oil qualityof the oil is lower than the oil quality threshold, operating thevehicle in a second mode that includes selectively deactivating thecylinder by trapping a high-pressure charge in the cylinder. In such amethod, operating the vehicle in the first mode further comprises,subsequent to deactivating the cylinder, providing a spark event to thecylinder when a piston coupled to the cylinder is within a threshold ofbottom dead center, where bottom dead center comprises a position of thepiston where the piston is nearest to a crankshaft of the variabledisplacement engine.

In one example of such a method, providing the spark event may be afunction of in-cylinder pressure. Furthermore, in some examples thespark event may be provided either once per an engine cycle, or twiceper the engine cycle, where the engine cycle includes an exhaust stroke,an intake stroke, a compression stroke, and a power stroke, and whereineach spark event includes one or more strikes of an ignition coil of aspark plug configured to provide the spark event. Still further, anignition energy of the spark event may be variable as a function ofvehicle operating conditions.

In another example of such a method, deactivating the cylinder in thesecond mode by trapping the high-pressure charge in the cylinder mayfurther comprise combusting a mixture of air and fuel in the cylinderwith the cylinder sealed from atmosphere, and then maintaining thecylinder sealed with combusted air and fuel trapped in the cylinder.

Still further, in such a method, both the first mode and the second modemay include stopping injection of fuel provided to the cylinder, andwherein the second mode may include additionally stopping providingspark to the cylinder.

The methodology with regard to FIGS. 3A-3B, along with the mapscorresponding to FIGS. 4-7 depict example scenarios for preventing sparkplug fouling when one or more cylinders of an engine are deactivated.Such methodology relies on providing spark near BDC for deactivatedcylinder(s), as discussed in detail above, to reduce or avoid unintendedcombustion events while the cylinder(s) are deactivated. However, it isrecognized herein that there may be circumstances where an unintendedcombustion event or events may still occur even under conditions wherespark is provided near BDC, and that in the event of such an occurrence,mitigating actions may be undertaken in order to reduce undesiredconsequences of such unintended combustion event(s). Accordingly, FIGS.8A-8B depict another embodiment or example of the methodology depictedat FIGS. 3A-3B, where the engine is monitored for unintended combustionevents while one or more cylinders are deactivated, and in response toan indication of unintended combustion event(s), mitigating actions areundertaken.

Thus, turning to FIG. 8A, it depicts a flowchart for a high-levelexample method 800 for reducing spark plug fouling during operation ofan engine in a VDE mode, where the mechanism for deactivating cylindersof the engine is a function of oil quality, and where mitigating actionsare undertaken in response to an indication of unintended combustionduring the operation of the engine in VDE mode. Method 800 will bedescribed in reference to the systems described in FIGS. 1-2, though itshould be understood that method 800 may be applied to other systemswithout departing from the scope of this disclosure. Method 800 may becarried out by a controller, such as controller 12, and may be stored asexecutable instructions in non-transitory memory. Instructions forcarrying out method 800 and the rest of the methods included herein maybe executed by the controller based on instructions stored on a memoryof the controller and in conjunction with signals received from sensorsof the vehicle system, such as the sensors described above withreference to FIGS. 1-2. The controller may employ engine systemactuators such as spark plug(s) (e.g. 192), fuel injector(s) (e.g. 166),etc., according to the methods depicted below.

It may be understood that there are a number of steps of method 800 thatare the same or essentially the same as steps of method 300 discussedabove. Thus, such steps will be briefly described at FIG. 8A forbrevity.

Method 800 begins at 802, and may include estimating and/or measuringengine operating conditions. These may include, for example, enginespeed, desired torque (for example, from a pedal-position sensor),manifold pressure (MAP), manifold air flow (MAF), BP, enginetemperature, catalyst temperature, intake temperature, spark timing, airtemperature, knock limits, etc.

Proceeding to 804, method 800 may include determining, based on theestimated operating conditions, an engine mode of operation (e.g., VDEor non-VDE) (see step 304 of method 300).

Proceeding to 806, method 800 may include confirming whether VDEconditions are met. In one example, cylinder deactivation conditions maybe confirmed when torque demand is less than a threshold. If cylinderdeactivation conditions are confirmed, a VDE mode is selected. Ifcylinder deactivation conditions are not confirmed, at 810, the routineincludes maintaining all the cylinders active and combusting.

If cylinder deactivation conditions and a VDE mode of operation areconfirmed, then method 800 may proceed to 812. At 812, method 800 mayinclude determining a quality of oil included in the engine forlubrication, cleaning, and cooling of various engine components. Asdiscussed above at step 312 of method 300, determining a quality of oilat 312 may include determining whether the quality of the oil is abovean oil quality threshold, or below the oil quality threshold, where oilquality above the threshold indicates higher (e.g. better) quality oil,and where oil quality below the threshold indicates lower (e.g. lesser)quality oil. Higher, or better, quality oil may comprise oil which ismore effective at lubricating, cleaning, and/or drawing heat from theengine, whereas lower quality, or lesser quality oil may comprise oilwhich is less effective at lubricating, cleaning, and/or drawing heatfrom the engine. What dictates the oil quality threshold, andcircumstances for adjusting such an oil quality threshold have beendiscussed in detail above at 312, and thus will not be reiterated herefor brevity.

At 812, if oil quality is indicated to be below the threshold, method800 may proceed to FIG. 8B, where deactivation of the one or more enginecylinder(s) may be conducted such that a pressure (positive pressurewith respect to atmospheric pressure), which may reduce the potentialfor spark plug fouling by reducing/preventing oil migration into thecylinder(s), is trapped in the cylinder(s). As discussed, a disadvantageto such a method may be a torque bump present at deactivation. Thus,where possible, it may be desirable to deactivate the cylinder(s) bytrapping a vacuum rather than a pressure.

Alternatively, at 812, in response to an indication that oil quality isgreater than the oil quality threshold, method 800 may proceed to 814.At 814, method 800 may include selecting one or more engine cylinders todeactivate based on the estimated engine operating conditions. In someexamples, a group of cylinders or a bank of cylinders may bedeactivated. The selection may be based on, for example, which cylinderor cylinders were deactivated during a previous VDE mode of operation.For example, if during the previous cylinder deactivation condition, afirst cylinder or first group of cylinders on a first engine bank weredeactivated, then a controller may select a second cylinder or a secondgroup of cylinders on a second engine bank for deactivation during thepresent VDE mode of operation. As another example, the selection may bebased on a regeneration state of a first exhaust catalyst (or emissioncontrol device) coupled to the first bank relative to the regenerationstate of a second exhaust catalyst (or emission control device) coupledto the second bank.

In still another example, which will be elaborated on below, determiningwhich cylinder(s) to deactivate at 814 may be a function of whetherparticular cylinder(s) are indicated to be prone to unintendedcombustion events when deactivated via trapping vacuum in thecylinder(s). For example, if a particular cylinder or cylinder(s) havepreviously been indicated to result in unintended combustion eventswhile deactivated, then such cylinder(s) may be prevented from beingdeactivated, while those other cylinder(s) that have not been indicatedas being susceptible to unintended combustion events may comprisecylinders which may be deactivated.

Following the selection, also at 814, the controller may selectivelydeactivate the one or more engine cylinders via trapping vacuum in theone or more cylinder(s), as discussed above. In this way, rather thantrapping a positive pressure with respect to atmospheric pressure or ahigh-pressure charge in the cylinder (see FIG. 3B), a vacuum (negativepressure with respect to atmospheric pressure) may be trapped in the oneor more selected cylinder(s). As discussed, trapping the vacuum in theone or more selected cylinder(s) may reduce or eliminate torque bump(s)at deactivation, but may lead to increased oil consumption, spark plugfouling, and/or undesired combustion events if appropriate mitigatingaction is not undertaken.

Thus, proceeding to 816, method 800 may include commanding spark to eachof the one or more deactivated engine cylinder(s) near BDC. As discussedabove, in one example, “near” BDC may comprise within 5 degrees or lessof BDC, within 10 degrees or less of BDC, or within 20 degrees or lessof BDC.

To determine whether a deactivated engine cylinder piston is near BDC(e.g. within a threshold of BDC), a crankshaft position sensor (e.g.120) and/or one or more camshaft sensor(s) (e.g. 188, 189) may beutilized.

At step 316 of method 300 discussed above at FIG. 3A, it was extensivelydiscussed as to how frequently spark may be provided near BDC, and howignition energy for each spark event may be adjusted. Thus, suchinformation will not be provided here for brevity, but it may beunderstood that the description above with regard to step 316 of method300 applies equally to step 816 of method 800.

As discussed, providing spark near BDC may prevent undesired fouling ofthe spark plug(s) corresponding to deactivated cylinder(s), andfurthermore, by providing spark near BDC unintended combustion eventsmay be reduced. However, there may be circumstances where an unintendedcombustion event or events still occur. Accordingly, in response to suchoccurrences, mitigating actions may be taken, the details of which areprovided in the continuing discussion with regard to the method of FIG.8A.

Thus, proceeding to 818, method 800 may include monitoring crankshaftacceleration. Crankshaft acceleration may be monitored, for example, atleast in part via a crankshaft position sensor (e.g. 120). Withcrankshaft acceleration being monitored at 818, method 800 may proceedto 820. At 820, method 800 may include indicating whether an unintendedcombustion event is detected. More specifically, an unintendedcombustion event may be indicated if crankshaft acceleration exceeds apredetermined crankshaft acceleration threshold. For example, thecrankshaft acceleration threshold may be a function of vehicle speed,engine speed, engine load, or other operating conditions that may affectcrankshaft acceleration. As one example, an expected crankshaftacceleration may be indicated via a lookup table stored at thecontroller, the lookup table a function of one or more of vehicle speed,engine speed, engine load, etc. Then, another lookup table may includeinformation as to what crankshaft acceleration threshold to utilize as afunction of the expected crankshaft acceleration. In some examples, thecrankshaft acceleration threshold may be a fixed amount of accelerationgreater than the expected crankshaft acceleration.

If, at 820, crankshaft acceleration is not greater than the crankshaftacceleration threshold, or in other words unintended combustion is notindicated, method 800 may proceed to 822. At 822, method 800 may includeindicating whether non-VDE mode conditions, or in other words,reactivation conditions, are met. As discussed above, reactivationconditions may be met when engine torque demand increases above athreshold. In another example, reactivation conditions may be consideredmet when the engine has operated in the VDE mode for a specifiedduration. Accordingly, at 822, non-VDE conditions may be confirmed. Ifnon-VDE conditions are not confirmed, the engine may continue to beoperated in the VDE mode with the selected deactivated one or morecylinders sealed (e.g. intake and exhaust valve(s) closed, with fuelingto the deactivated cylinder(s) stopped, and with spark being provided tothe one or more deactivated cylinders near BDC occasions.

Alternatively, upon confirming non-VDE conditions at 822, thedeactivated cylinder(s) may be reactivated at 830. Specifically, thedeactivated fuel injector(s) may be reactivated, and spark may beprovided to the deactivated engine cylinder(s). Reactivation of thedeactivated engine cylinder(s) may comprise commanding spark to thereactivated cylinder(s) near TDC (e.g. just prior or within a thresholdnumber of degrees of TDC).

In response to reactivation of the engine cylinders at 830, method 800may proceed to 832. At 832, method 800 may include updating vehicleoperating parameters. For example, updating vehicle operating parametersat 832 may include storing information collected during the time thatthe engine was operated in the VDE mode at the controller. Morespecifically, such information may include whether or not unintendedcombustion events were detected, or not. In an example where nounintended combustion events were detected, such information may bestored at the controller, in order to indicate that no particular enginecylinders are, at the moment, prone or susceptible to unintendedcombustion events. Thus, updating vehicle operating parameters at 832may include not specifying any particular engine cylinder as beingsusceptible or prone to unintended combustion events while deactivatedwith trapped vacuum. However, updating vehicle operating parameters at832 may include storing information as to which engine cylinder(s) weredeactivated, such that for a subsequent time when a request to operatethe engine in VDE mode is indicated, remaining cylinder(s) may bedeactivated while the recently deactivated cylinders may be keptactivated. Method 800 may then end.

Returning to 820, in response to an indication of unintended combustion,method 800 may proceed to 824. At 824, method 800 may includedetermining a next firing cylinder, where the next firing cylinderincludes the very next cylinder expected or scheduled to fire subsequentto the unintended combustion event. Such an indication may be based onfiring order of the activated cylinders, in one example.

With the next firing cylinder determined at 824, method 800 may proceedto 826. At 826, method 800 may include retarding spark for thedetermined next firing cylinder. Retarding spark at 826 may be afunction of the crankshaft acceleration indicated at 820, for example.More specifically, based on the crankshaft acceleration indicated at820, an amount of increased torque provided via the engine due to theunintended combustion may be determined. In order to offset thisincreased torque, to thus make torque output of the engine equal to anaverage requested torque output, spark to the next firing cylinder maybe retarded a determined amount. In this way, a torque bump that wouldtypically occur as a result of the unintended combustion event, may bereduced or avoided altogether.

Subsequent to mitigating the torque bump that may otherwise occur ifspark is not retarded for the cylinder scheduled to fire next after theunintended combustion event, method 800 may proceed to 828. At 828,method 800 may include setting the deactivated cylinder(s) to become theactivated, firing cylinders, whereas the activated cylinders may bedeactivated. In other words, the firing and non-firing (deactivated)cylinder(s) may be set to another group of firing and non-firingcylinders. It may be understood that setting the deactivated cylinder(s)to become activated cylinders while deactivating the currently activatedcylinders may comprise keeping a total torque output the same as priorto the switching of cylinder status.

At 828, reactivation of the cylinder that was indicated as producingunintended combustion may be conducted as follows. First, the exhaustvalve may be opened, thus clearing the cylinder with unintendedcombustion of residual burnt gas due to the unintended combustion, priorto inducting an air/fuel charge and providing spark to the particularcylinder.

Once the mitigating actions have been undertaken to avoid the torquebump due to unintended combustion, and to clear residual burnt gas fromthe cylinder that produced the unintended combustion, method 800 maycontinue to monitor crankshaft acceleration in order to indicate whetherany more unintended combustion events are detected. In a case whereanother unintended combustion event is indicated, while not explicitlyillustrated, it may be understood that steps 824-828 may again beconducted, but where a deactivated cylinder that previously wasindicated as being a source of unintended combustion may not be selectedfor reactivation during the switching of deactivated to reactivatedcylinders, and vice versa, at step 828. In other words, any cylinderindicated as being susceptible or prone to unintended combustion may bedesignated as a cylinder that may not be selected for deactivation.

In the absence of further unintended combustion events, method 800 mayproceed to 822, where it may be indicated as to whether non-VDE modeconditions are met. If not, method 800 may return to 816, where sparkmay be provided near BDC for deactivated cylinder(s), and wherecrankshaft acceleration may continue to be monitored in order toindicate any unintended combustion events.

Returning to 822, responsive to non-VDE mode conditions being indicatedto be met, method 800 may proceed to 830. As discussed, at 830, method800 may include reactivating the deactivated engine cylinders. Morespecifically, fueling and spark may be resumed to the deactivatedcylinders. It may be understood that when reactivating the deactivatedcylinders, even though such cylinders may not have experienced anunintended combustion event, there may be crankcase vapors and/or oilmigration into the cylinder that may have occurred. Thus, forreactivation of the cylinders, in some examples the contents of thecylinder(s) may be first exhausted to the exhaust system via opening theexhaust valve coupled to such cylinder(s), prior to inducting anair/fuel charge and providing spark to reactivate such cylinder(s).

Proceeding to 832, method 800 may include updating vehicle operatingparameters. More specifically, updating vehicle operating parameters at832 may include storing information at the controller as to whichparticular cylinder or cylinders are prone to unintended combustionevents, such that at a subsequent time when VDE-mode conditions are met,such cylinders are not deactivated. In other words, the controller maydesignate engine cylinders that have been indicated to be prone tounintended combustion, as non-deactivatable until the vehicle has beenserviced via a technician and until the issues related to the unintendedcombustion have been mitigated. Thus, in some examples, a malfunctionindicator light (MIL) may be illuminated at the vehicle dash, indicatingwhich cylinder(s) resulted in unintended combustion, such that suchundesired effects may be mitigated. Method 800 may then end.

Returning to 812, in a case where oil quality is indicated as beingbelow the oil quality threshold, method 800 may proceed to FIG. 8B, asdiscussed. Accordingly, turning to FIG. 8B, it depicts an example method850 for deactivating particular engine cylinders by trapping a positivepressure with respect to atmospheric pressure in the cylinder(s) set fordeactivation. Furthermore, such a method may include conducting a sparkplug cleaning routine while the cylinders are deactivated, provided thatconditions are indicated to be met for conducting such a routine. Asmethod 850 stems from method 800, method 850 will be described inreference to the systems described in FIGS. 1-2, though it should beunderstood that method 850 may be applied to other systems withoutdeparting from the scope of this disclosure. Method 850 may be carriedout by a controller, such as controller 12, and may be stored asexecutable instructions in non-transitory memory. Instructions forcarrying out method 850 and the rest of the methods included herein maybe executed by the controller based on instructions stored on a memoryof the controller and in conjunction with signals received from sensorsof the vehicle system, such as the sensors described above withreference to FIGS. 1-2. The controller may employ engine systemactuators such as spark plug(s) (e.g. 192), fuel injector(s) (e.g. 166),etc., according to the methods depicted below.

Method 850 begins at 855, and may include determining which cylinder(s)to deactivate. As discussed above in detail at step 314 of FIG. 3A, insome examples a group of cylinders or a bank of cylinders may bedeactivated, where such selection may be based on which cylinder orcylinders were deactivated during a previous VDE mode of operation. Inother examples, the selection may be additionally or alternatively basedon a regeneration state of a first exhaust catalyst or emission controldevice coupled to the first bank relative to the regeneration state of asecond exhaust catalyst or emission control device coupled to the secondbank. Still further, in other examples, the selection may additionallyor alternatively be based on whether or not a particular cylinder orcylinders of the engine are indicated as being prone or susceptible tounintended combustion while deactivated. More specifically, in oneexample, cylinder(s) that are indicated as being prone to unintendedcombustion while deactivated may be designated as cylinder(s) thatcannot be deactivated. Such an example may include cylinder(s) indicatedto be prone to unintended combustion under conditions where thecylinder(s) are deactivated via trapping vacuum, or trapping positivepressure. In other examples, if a particular cylinder or cylinders areindicated as being prone to unintended combustion when deactivated viatrapping vacuum, such a cylinder or cylinders may still be deactivatedvia trapping positive pressure. In other words, the conditions that ledto unintended combustion when the cylinder or cylinder(s) weredeactivated with trapped vacuum may not inherently result in unintendedcombustion when the cylinder is deactivated in a different way (trappingpositive pressure versus vacuum), and thus, in some examples a cylinderor cylinders that exhibit unintended combustion when deactivated viatrapping vacuum may be deactivated via trapping positive pressure.However, in other examples, as discussed, if a cylinder or cylinders areindicated to result in unintended combustion while deactivated,regardless of how the deactivation is conducted (e.g. trapping vacuum ortrapping positive pressure), then such a cylinder or cylinders may bedesignated as non-deactivatable.

With the cylinder(s) determined to be deactivated at 855, method 850 mayproceed to 860. At 860, method 850 may include deactivating the selectedcylinders to trap positive pressure in the cylinder(s). It may beunderstood that there may be two ways of trapping positive pressure in acylinder selected for deactivation. In one example, an air charge may beinducted into the cylinder via an open intake valve, but rather thanprovided fueling and spark, the air charge may be trapped in thecylinder via closing the intake valve, without correspondingly openingthe exhaust valve. In some examples, such an approach may be utilizedprovided that oil quality is less than the oil quality threshold, butgreater than a second oil quality threshold. The second example of how apositive pressure may be trapped in the cylinder may comprise inductingan air/fuel charge, and providing spark, but not exhausting thecombusted air and fuel, thus trapping a high pressure charge. Suchexamples have been discussed above in detail with regard to FIG. 3B.

Thus, as discussed, at 860, method 850 may include trapping positivepressure with respect to atmospheric pressure in one or more cylindersselected for deactivation. Proceeding to 865, method 850 may includeindicating whether conditions are met for spark plug cleaning or not. Itmay be understood that, in this example, spark plug cleaning maycomprise providing spark to deactivated cylinder(s), such that sparkplug fouling may be reduced or avoided. When trapping positive pressurein the cylinder, such potential for spark plug fouling may be reduced ascompared to when a cylinder or cylinders are deactivated via trappingvacuum, due to the lowered potential for crankcase vapors and oilmigration to the deactivated cylinder(s). However, over time positivepressure in deactivated cylinder(s) may bleed down, the cylinder(s) maycool, and as such, migration of oil and crankcase vapors may be morelikely. Thus, conditions being met for spark plug cleaning may include athreshold duration of time elapsing since the cylinder(s) weredeactivated. Conditions being met for spark plug cleaning mayadditionally or alternatively include an indication that a thresholdnumber of engine cycles has occurred since the cylinder(s) weredeactivated.

If, at 865, conditions are not indicated to be met for conducting sparkplug cleaning, method 850 may proceed to 868, where it may be indicatedas to whether non-VDE mode conditions are met. As discussed above,non-VDE mode conditions (e.g. reactivation conditions) may be met whenengine torque demand increases above a threshold. In another example,reactivation conditions may be considered met when the engine hasoperated in the VDE mode for a specified duration. Accordingly, at 868,non-VDE conditions may be confirmed. If non-VDE conditions are notconfirmed, the engine may continue to be operated in the VDE mode withthe selected one or more cylinders deactivated (e.g. intake and exhaustvalve(s) closed, with fueling to the deactivated cylinder(s) stopped).

Alternatively, upon confirming non-VDE conditions at 868, thedeactivated cylinder(s) may be reactivated at 870. Specifically, thedeactivated fuel injector(s) may be reactivated, and spark may beprovided to the deactivated engine cylinder(s). Reactivation of thedeactivated engine cylinder(s) may comprise commanding spark to thereactivated cylinder(s) near TDC (e.g. just prior or within a thresholdnumber of degrees of TDC).

In response to reactivation of the engine cylinders at 870, method 850may proceed to 872. At 872, method 850 may include updating vehicleoperating parameters. For example, updating vehicle operating parametersat 872 may include storing information collected during the time thatthe engine was operated in the VDE mode at the controller. Morespecifically, such information may include what cylinder(s) weredeactivated, how long the deactivation of cylinder(s) occurred, and thatconditions were not met for spark plug cleaning. Such information may bestored at the controller, and may be utilized for subsequent cylinderdeactivation events.

Returning to 865, in response to conditions being met for spark plugcleaning, method 850 may proceed to 876. At 876, method 850 may includeproviding spark near BDC for each cylinder that has been selectivelydeactivated, as discussed above at step 816 of method 800. The remainingsteps (878-886) of method 850 have been described above at method 800with regard to steps 818-828), and thus will only be described brieflyhere. With spark provided near BDC at 876, method 800 may includemonitoring crankshaft acceleration at 878. Proceeding to 880, inresponse to crankshaft acceleration greater than the predeterminedcrankshaft acceleration threshold discussed above, or in other words, inresponse to an unintended combustion event, method 850 may proceed to882. At 882, method 850 may include determining the next firing cylinderbased on firing order of activated cylinders, and at 884 method 850 mayinclude retarding spark for the determined next firing cylinder, suchthat an average torque from the unintended and reduced torque combustionevent (from the retarded spark on the next firing cylinder) is equal toan average requested torque output of the engine. By retarding spark forthe determined next firing cylinder, a torque bump that would otherwisebe present due to the unintended combustion, may be reduced or avoided.

Proceeding to 886, method 800 may include reactivating deactivatedcylinder(s), and reassigning cylinders to be deactivated. In thisexample method 850, it may be understood that deactivating cylinders mayinclude trapping positive pressure in the selected cylinder(s), asopposed to trapping vacuum in the cylinder(s), as oil quality is belowthe oil quality threshold. In reactivating the deactivated cylinder thatwas the source of the unintended combustion event, it may be understoodthat the residual burnt gas from the unintended combustion event mayfirst be exhausted to the exhaust system, prior to inducting an air/fuelcharge and initiating combustion by providing spark.

Furthermore, it may be understood that, in reassigning cylinders to bedeactivated, and cylinders to be activated, any cylinder(s) previouslyindicated to be prone to unintended combustion may be designated asnon-deactivatable. In other words, such cylinders may remain activatedduring the reassigning of cylinders at step 886 of method 850. However,as discussed, in other examples such action may depend on whether suchcylinder(s) were previously indicated to be susceptible to unintendedcombustion while deactivated via trapping vacuum, or deactivated viatrapping positive pressure in the cylinder(s). In some examples wherethe cylinder(s) have previously been implicated as being prone tounintended combustion, but where such an indication occurred while thecylinder(s) were deactivated to trap vacuum, then such cylinder(s) maybe prevented from being deactivated to trap vacuum, but may still bedeactivated to trap positive pressure. However, in such an example, anycylinder(s) previously indicated to be prone to unintended combustionwhile deactivated to trap positive pressure, may be prevented from beingdeactivated subsequently either via trapping vacuum or positivepressure. In any event, responsive to mitigating the torque bump due tounintended combustion, and further responsive to reassigning enginecylinders for deactivation/reactivation, method 850 may continue tomonitor crankshaft acceleration for unintended combustion events.

Under conditions where further unintended combustion events are notindicated, method 850 may proceed to 868, and may include indicatingwhether non-VDE mode conditions are met, as discussed above. If not,method 850 may continue to operate the engine in the VDE mode ofoperation. Alternatively, in response to non-VDE conditions being met,method 850 may proceed to 870, and may include reactivating thedeactivated cylinder(s) via providing fuel and spark to saidcylinder(s).

Proceeding to 872, method 850 may include updating vehicle operatingparameters. Updating vehicle operating parameters at 872 may includestoring at the controller which cylinder(s) produced unintendedcombustion event(s) during operating the engine in the VDE mode. Suchinformation may be utilized for subsequent cylinder deactivation events.In some examples, updating vehicle operating parameters at 872 mayinclude setting a MIL at the dash, to alert a vehicle operator of arequest to service the vehicle. Furthermore, updating vehicle operatingparameters at 872 may include designating one or more cylinders as beingnon-deactivatable, due to the unintended combustion event(s). Morespecifically, because unintended combustion was detected even when apositive pressure was trapped in the cylinder(s), then it may be highlylikely that unintended combustion may occur subsequently if vacuum weretrapped in the cylinder at deactivation, or if positive pressure wereagain trapped at deactivation. Thus, while in some examples a cylinderthat exhibited unintended combustion under conditions where the cylinderwas deactivated by trapping vacuum may still be deactivated via trappingpositive pressure, in a situation where unintended combustion wasdetected under conditions where positive pressure was trapped atdeactivation, such a cylinder may be designated as non-deactivatable, asdiscussed.

While the above description with regard to methods of FIGS. 8A-8Binclude methods for reducing a torque bump resulting from unintendedcombustion in engine cylinders where, in some examples, spark isprovided near BDC for deactivated cylinders, it may be understood thatsuch methodology may not be limited to conditions where spark isprovided near BDC for deactivated cylinders. In some examples, suchmethodology may be utilized under conditions where spark is provided atother predetermined positions that do not necessarily include sparkingnear BDC (e.g. within the threshold number of degrees of BDC). In otherwords, such methodology for reducing a torque bump and for reassigningactivated/deactivated cylinders subsequent to the unintended combustionis not limited to situations where spark is provided to deactivatedcylinder(s) near BDC, without departing from the scope of thisdisclosure.

Furthermore, it is herein recognized that determining whether to trapnegative pressure or positive pressure in the cylinder(s) scheduled fordeactivation may be in some examples independent of oil quality, withoutdeparting from the scope of this disclosure. In other words, methods forreducing or avoiding a torque bump resulting from unintended combustionin a deactivated cylinder may be applicable to deactivated cylindersthat have been deactivated independent of oil quality (via trappingpositive pressure or negative pressure at deactivation). Furthermore, insome examples, methods for reducing or avoiding spark plug fouling maybe conducted irrespective of oil quality, without departing from thescope of this disclosure.

Thus, the methods of FIGS. 8A-8B may enable a method comprisingdeactivating a subset of cylinders of a variable displacement enginewhile other cylinders of the engine combust air and fuel, reducing oravoiding a torque bump due to an unintended combustion event in adeactivated cylinder by reducing a torque output of the engine andreactivating the deactivated cylinder which had the unintendedcombustion event, and during subsequent cylinder deactivation events,not deactivating the cylinder which had the unintended combustion event.In this way, under conditions where an unintended combustion eventoccurs while operating the engine with deactivated cylinders, a torquebump associated with the unintended combustion event may be reduced oravoided, which may improve engine efficiency and which may improvecustomer satisfaction.

In one example of the method, the unintended combustion event includesan acceleration of a crankshaft coupled to the engine greater than athreshold crankshaft acceleration. Furthermore, in some examples, themethod may include exhausting residual burnt gas from the deactivatedcylinder with the unintended combustion event prior to reactivating thedeactivated cylinder with the unintended combustion event.

In another example of the method, reducing the torque output of theengine may comprise reducing a torque contribution of an activatedcylinder that is scheduled to combust air and fuel immediately followingthe unintended combustion event. In such an example, reducing the torquecontribution of the activated cylinder may further comprise retarding aspark provided to the activated cylinder for combustion of air and fuel,where an amount that the spark is retarded is a function of a torqueincrease provided to the engine via the unintended combustion event.

Still further, in an example of the method, the method may furthercomprise deactivating the subset of cylinders of the engine via trappingeither a negative pressure with respect to atmospheric pressure or apositive pressure with respect to atmospheric pressure in the subset ofcylinders. As one example, trapping the negative pressure may be inresponse to an indication that an oil quality of an oil utilized forcooling, lubrication and/or cleaning of the engine is greater than anoil quality threshold, and wherein trapping the positive pressure may bein response to an indication that the oil quality of the oil is belowthe oil quality threshold. Furthermore, such a method may compriseproviding spark to the subset of deactivated cylinders at apredetermined position of one or more pistons coupled to the subset ofdeactivated cylinders, wherein providing spark may further be a functionof pressure in the subset of deactivated cylinders, and whereinproviding spark may serve to prevent fouling of one or more spark plugsconfigured to provide spark to the subset of deactivated cylinders. Inone example, the predetermined position of the one or more pistons mayinclude a position within a threshold number of degrees from a bottomdead center position.

Finally, in an example of the method, the engine may comprise a variabledisplacement engine. In such an example, reactivating the deactivatedcylinder may further comprise reactivating the subset of deactivatedcylinders including the deactivated cylinder which had the unintendedcombustion event, and deactivating the other cylinders of the engineoperating to combust fuel.

Another example of a method may comprise, with a first set of cylindersof an engine deactivated and with a second set of cylinders activated tocombust air and fuel, monitoring acceleration of a crankshaft coupled tothe engine. In response to acceleration of the crankshaft greater than acrankshaft acceleration threshold, the method may include retarding aspark provided via an activated cylinder included in the second set ofcylinders, the activated cylinder comprising a cylinder scheduled tocombust air and fuel immediately following the acceleration of thecrankshaft greater than the crankshaft acceleration threshold. Themethod may further include reactivating a deactivated cylinderresponsible for the acceleration of the crankshaft greater than thecrankshaft acceleration threshold and deactivating a cylinder from thesecond set of cylinders.

In such a method, retarding the spark may includes retarding the spark adetermined amount, the determined amount a function of an amount ofacceleration of the crankshaft. Furthermore, in such a method, retardingthe spark may offset a torque increase of the engine due to accelerationof the crankshaft greater than the crankshaft acceleration threshold,which in turn may reduce or avoid a torque bump otherwise associatedwith the torque increase of the engine.

Such a method may further comprise reactivating all of the first set ofdeactivated cylinders, and deactivating all of the second set ofactivated cylinders, just after retarding the spark provided via theactivated cylinder included in the second set of cylinders.

Furthermore, in such a method, residual burnt gas from the deactivatedcylinder responsible for the acceleration of the crankshaft greater thanthe crankshaft acceleration threshold is first exhausted from thedeactivated cylinder just prior to reactivating the deactivatedcylinder.

Still further, in such a method, deactivating the first set of cylindersmay include stopping fuel injection and sealing the first set ofcylinders, and may further comprise providing spark to the first set ofdeactivated cylinders at a predetermined position of one or more pistonscoupled to the first set of deactivated cylinders, where providing sparkmay be a function of at least pressure in the first set of deactivatedcylinders.

Turning now to FIG. 9, an example map 900 is shown. Specifically, map900 depicts a drive cycle where a particular cylinder is deactivated bytrapping vacuum in the cylinder, and where spark plug cleaning isconducted by providing spark at BDC while the cylinder is deactivated.Further, map 900 depicts an unintended combustion event while thecylinder is deactivated, thus map 900 further depicts exhaustingresidual burnt gas from the combustion event and then reactivating thecylinder subsequent to the unintended combustion event. Similar to thatdiscussed above at FIGS. 4-7, a single engine cylinder is depicted atFIG. 9, for clarity. Map 900 includes a number of engine cycles thatinclude four strokes, depicted as E, I, C, and P, corresponding toexhaust, intake, compression, and power strokes, respectively.Furthermore, similar to FIGS. 4-7, map 900 illustrates engine position,showing where TDC (T) and BDC (B) are in relation to each engine cycle.Map 900 includes plot 905, indicating valve timing. For example map 700,it may be understood that a valve shown opening and closing during theexhaust stroke (E) corresponds to an exhaust valve 906 for the cylinder,and a valve shown opening and closing during the intake stroke (I)corresponds to an intake valve 907 for the cylinder. Map 900 furtherincludes plot 910, indicating piston position in relation to the enginecycles. Map 900 further includes plot 915, indicating spark ignitionenergy, in relation to the engine cycles. Map 900 further includes plot920, indicating whether fuel injection to the engine cylinder is on, oroff, in relation to the engine cycles. Map 900 further includes plot925, indicating whether an unintended combustion event is indicated, inrelation to the engine cycles.

It may be understood that map 900 depicts a portion of a single drivecycle, the portion of the single drive cycle divided up into threesegments, which will be elaborated upon below.

Segment 1 illustrates a portion of the drive cycle where VDE conditionsare met, and, while not explicitly illustrated, it may be understoodthat oil quality is above the threshold oil quality. Furthermore, it maybe understood that the cylinder illustrated at map 900 comprises acylinder selected for deactivation. Accordingly, with oil quality abovethe threshold, the exhaust valve opens and then closes, to deactivatethe cylinder. In other words, it may be understood that the exhaustvalve opens to route combusted gases out of the cylinder, and then theexhaust valve closes, thus trapping a vacuum in the cylinder. Asdiscussed above, trapping vacuum inside the cylinder may result in oilmigration to the cylinder, which may result in fouling of the sparkplug. Thus, to mitigate such an issue, as illustrated at map 900, sparkis provided at every other BDC occasion while the cylinder isdeactivated. It may be understood in example map 900 that the sparkprovided comprises the basal spark ignition energy. By continuing tospark near BDC while fueling is cut off from the deactivated cylinder,and with the vacuum trapped in the sealed cylinder (intake and exhaustvalves closed), fouling of the spark plug may be prevented or reducedduring segment 1 of the drive cycle.

However, during segment 2 of the portion of the drive cycle representedby map 900, an unintended combustion event is detected (plot 925). Asdiscussed above, unintended combustion may be indicated via crankshaftacceleration greater than a predetermined crankshaft accelerationthreshold while the engine is operating in VDE mode. Accordingly, asdiscussed above with regard to method 800 depicted at FIG. 8A, thecylinder is reactivated during segment 3 of the portion of the drivecycle depicted by map 900. More specifically, in response to theindication of unintended combustion, the cylinder is reactivated duringsegment 3 by first opening the exhaust valve, which may exhaust residualburnt gas from the cylinder. Once the residual burnt gas from theunintended combustion event is exhausted, the induction of air andfueling is resumed. Furthermore, spark is provided near TDC, of thecompression stroke, instead of BDC. Thus, for the remainder of segment3, the previously deactivated cylinder is activated to combust air andfuel. Furthermore, while fuel injection to the reactivated cylinder isillustrated as occurring during the compression stroke, fuel injectionmay be provided during the intake stroke.

In this way, a deactivated cylinder that experiences unintendedcombustion while providing spark near BDC may be reactivated in a waythat ensures residual burnt gas from the unintended combustion eventdoes not remain in the cylinder upon reactivation, thus increasing alikelihood for achieving desired combustion efficiency uponreactivation.

Thus, map 900 specifically depicts how a particular deactivated cylindermay be reactivated in response to an indication of unintendedcombustion. For clarity, only a single engine cylinder is depicted atmap 900. However, as discussed above with regard to FIG. 8A, theunintended combustion while a cylinder is deactivated may result in atorque bump, if mitigating action is not undertaken. Such mitigatingaction may include retarding spark on the next cylinder scheduled forfiring after the unintended combustion event, as discussed. Accordingly,FIG. 10 depicts an example timeline 1000 depicting how mitigating actionmay be taken to reduce or avoid the torque bump that would otherwise bepresent in response to unintended combustion while the engine is beingoperated in VDE-mode.

Thus, turning to FIG. 10, example timeline 1000 includes plot 1005,depicting valve timing for a first cylinder (C1) of an engine, overtime. Illustrated for plot 1005 is a number of strokes of the engine,including exhaust (E), intake (I), compression (C), and power (P)strokes. Exhaust valve opening/closing is depicted by line(s) 1006,occurring during the exhaust stroke, while intake valve opening/closingis depicted by line(s) 1007, occurring during the intake stroke.Timeline 1000 further includes plot 1010, indicating piston position fora piston coupled to C1, over time. The piston may be at top dead center(TDC), bottom dead center (BDC), or somewhere in between. Timeline 1000further includes plot 1015, indicating spark energy provided via a sparkplug coupled to C1, over time. Timeline 1000 further includes plot 1020,indicating fuel injection provided to C1, over time. Timeline 1000further includes plot 1025, indicating whether unintended combustion forC1 is indicated, over time. Unintended combustion may be indicated, asdiscussed, via monitoring crankshaft acceleration while the engine isbeing operated in VDE-mode. In response to crankshaft accelerationgreater than a predetermined crankshaft acceleration threshold, anunintended combustion event may be indicated.

Timeline 1000 further includes plot 1030, indicating valve timing for asecond cylinder (C2) of the engine, over time. Illustrated for plot1030, similar to that of plot 1005, is a number of strokes of theengine, including exhaust (E), intake (I), compression (C), and power(P) strokes. Exhaust valve opening/closing is depicted by line(s) 1032,while intake valve opening/closing is depicted by line(s) 1031. Timeline1000 further includes plot 1035, indicating piston position for a pistoncoupled to C2, over time. The piston may be at TDC, BDC, or somewhere inbetween. Timeline 1000 further includes plot 1040, indicating sparkenergy provided via a spark plug coupled to C2, over time. As will bediscussed below, mitigating action in response to unintended combustionwhile the engine is operating in VDE mode may include retarding sparkfor C2, thus a non-retarded spark position is indicated, for clarity,via dashed plot 1045. Timeline 1000 further includes plot 1050,indicating fuel injection provided to C2, over time.

It may be understood that C1 and C2 are arbitrary designations, andspecifically, as will be discussed below, C1 comprises a cylinder thatis deactivated but which experiences unintended combustion whiledeactivated. C2 comprises the next firing cylinder, or cylinderscheduled to fire just after the unintended combustion event hasoccurred for C1. Other cylinders of the engine may be deactivated, andstill others may be activated, as discussed above. In other words, onlyC1 and C2 are shown for clarity.

At time t0, it may be understood that C1 is already deactivated (plot1005), with vacuum trapped in the cylinder. Accordingly, between time t0and t1, exhaust valve (line 1006) and intake valve (line 1007) aremaintained closed, thus maintaining C1 sealed. With C1 deactivated totrap vacuum, in this example timeline 1000, spark is provided near BDCat every other BDC occasion.

Further, at time t0, C2 is activated, or in other words is in operationto combust air and fuel. Thus, the exhaust valve (line 1032) opensduring the exhaust stroke between time t0 and t1, and the intake valve(line 1031) opens during the intake stroke between time t0 and t1.Further, fuel (plot 1050) and spark (plot 1040) is provided to C2between time t0 and t1. In this example timeline 1000, fuel is providedduring the intake stroke. However, in other examples fuel may beprovided during the compression stroke, without departing from the scopeof this disclosure.

At time t1, unintended combustion is detected corresponding tounintended combustion at C1. With unintended combustion indicated at C1,the next firing cylinder (C2) is determined via the controller. Tomitigate a potential torque bump due to the unintended combustion event(the torque bump resulting from crankshaft acceleration greater thandesired), spark is retarded to C2 at time t2, immediately following theunintended combustion event at time t1. For illustrative purposes,non-retarded spark timing is illustrated by plot 1045. By retardingspark (corresponding to a reduced torque combustion event) for the nextfiring cylinder C2 after the C1 unintended combustion event, an averagetorque from the unintended combustion event and the reduced torquecombustion event may be equal to an average requested torque output ofthe engine. In this way, the torque bump that may otherwise result fromunintended combustion, may be reduced or avoided.

Mitigating action in response to the unintended combustion event mayfurther include reactivating the deactivated cylinder responsible forthe unintended combustion event, and deactivating another cylinder. Asdiscussed above, in some examples, such action may include reactivatingthe deactivated cylinder responsible for the unintended combustionevent, and reactivating any other deactivated cylinders (not responsiblefor the unintended combustion). Such action may further includedeactivating more than one cylinder that is activated. In other words,one set of deactivated cylinder may be reactivated, and another set ofactivated cylinders may be deactivated. In this example timeline 1000,only two cylinders are shown, for clarity.

Thus, reactivating the deactivated cylinder may include, at time t3,subsequent to taking mitigating action to reduce or avoid the torquebump, opening the exhaust valve corresponding to C1, thus exhaustingresidual burnt gas from C1. Responsive to exhausting the residual burntgas from C1, at time t4 the intake valve corresponding to C1 opens,drawing air into C1. At time t5, fuel is provided to C1, and at time t6,spark is provided to C1 near when the piston coupled to C1 is near TDC.Between time t6 and t7, C1 remains activated to combust air and fuel.

Returning to time t4, subsequent to retarding spark for C2 in order tomitigate the torque bump due to unintended combustion at C1, C2 isscheduled for deactivation. In this example timeline, the deactivationcorresponds to trapping vacuum in the cylinder. Accordingly, at time t4,the exhaust valve (line 1032) is opened and then closed, andsubsequently, the intake valve is not opened. After deactivation of C2,between time t4 and t7, spark is provided to the deactivated C2 nearevery other BDC occasion, in order to prevent spark plug fouling of C2.Furthermore, while not explicitly illustrated, it may be understood thatno unintended combustion events are detected at deactivated C2 for theduration of timeline 1000. Furthermore, it may be understood thattimeline 1000 depicts a situation where only a portion of the drivecycle is shown, and thus reactivation of C2 in response to non-VDEconditions being indicated is not illustrated. However, it may beunderstood that upon indication of non-VDE mode conditions being met, C2(and any other deactivated cylinders), may be reactivated as discussedabove.

In this way, spark plug fouling may be prevented while enablingdeactivation of engine cylinders without an undesirable torque bump thatwould otherwise be present if a high-pressure charge were trapped in thecylinder selected for deactivation, as opposed to trapping vacuum.Prevention or reduction of spark plug fouling may increase enginelifetime, increase fuel economy, and increase customer satisfaction.

The technical effect is to recognize that by continuing to spark nearBDC when a cylinder or cylinders are deactivated, spark plug fouling maybe prevented under conditions when a vacuum is trapped in thecylinder(s) upon deactivation. A further technical effect is torecognize that preventing spark plug fouling by providing spark may bedependent on vehicle operating conditions such as vehicle speed, enginespeed, engine load, battery SOC, etc., such that a frequency of sparkevents near BDC may vary depending on operating conditions. A stillfurther technical effect is to recognize that there may be circumstanceswhere it is preferable or desirable to trap a high-pressure charge in acylinder selected for deactivation, rather than trap vacuum, where suchcircumstances may include conditions where oil quality is degraded tobelow an oil quality threshold.

The systems described herein, and with reference to FIGS. 1-2, alongwith the methods described herein, and with reference to FIGS. 3A-3B,may enable one or more systems and one or more methods. In one example,a method comprises reducing fouling of a spark plug in a cylinder of anengine configured to propel a vehicle by providing a spark to thecylinder after the cylinder has been deactivated, where the spark isprovided when a piston coupled to the cylinder is within a threshold ofbottom dead center. In a first example of the method, the method furtherincludes where bottom dead center comprises a position of the pistonwhere the piston is nearest to a crankshaft of the engine. A secondexample of the method optionally includes the first example, and furtherincludes wherein the threshold of bottom dead center includes the pistonbeing within a predetermined number of degrees from bottom dead center,and where the predetermined number of degrees comprises within fivedegrees or less of bottom dead center, within ten degrees or less ofbottom dead center, or within twenty degrees or less of bottom deadcenter. A third example of the method optionally includes any one ormore or each of the first and second examples, and further includeswherein the engine comprises a variable displacement engine. A fourthexample of the method optionally includes any one or more or each of thefirst through third examples, and further includes wherein providing thespark to the cylinder after the cylinder has been deactivated occurs inresponse to the cylinder being deactivated via trapping a negativepressure with respect to atmospheric pressure in the cylinder atdeactivation. A fifth example of the method optionally includes any oneor more or each of the first through fourth examples, and furtherincludes wherein trapping the negative pressure at deactivation includesexhausting a combusted mixture of air and fuel to an exhaust system ofthe engine, and then sealing the cylinder from atmosphere. A sixthexample of the method optionally includes any one or more or each of thefirst through fifth examples, and further includes wherein deactivatingthe cylinder includes stopping providing a fuel to the cylinder. Aseventh example of the method optionally includes any one or more oreach of the first through sixth examples, and further includes whereinunder conditions where a plurality of cylinders are selected fordeactivation, providing spark to the plurality of cylinders in responseto deactivation of the plurality of cylinders, at the predefinedposition of a plurality of pistons coupled to the plurality ofcylinders. An eighth example of the method optionally includes any oneor more or each of the first through seventh examples, and furtherincludes wherein a spark ignition energy comprising the spark providedto the cylinder after deactivation of the cylinder is variable. A ninthexample of the method optionally includes any one or more or each of thefirst through eighth examples, and further comprises increasing thespark ignition energy after a predetermined number of spark events whilethe cylinder is deactivated. A tenth example of the method optionallyincludes any one or more or each of the first through ninth examples,and further includes wherein a spark frequency of the spark provided tothe cylinder is variable as a function of vehicle operating conditions.

Another example of a method comprises in a first operating condition ofa vehicle propelled by a variable displacement engine, including anindication that an oil quality of an oil utilized for cooling,lubrication and/or cleaning of the variable displacement engine isgreater than an oil quality threshold, operating the vehicle in a firstmode that includes selectively deactivating a cylinder of the variabledisplacement engine by trapping a vacuum in the cylinder; in a secondoperating condition of the vehicle, including an indication that the oilquality of the oil is lower than the oil quality threshold, operatingthe vehicle in the second mode that includes selectively deactivatingthe cylinder by trapping a high-pressure charge in the cylinder; andwhere operating the vehicle in the first mode further comprises,subsequent to deactivating the cylinder, providing a spark event to thecylinder when a piston coupled to the cylinder is within a threshold ofbottom dead center, where bottom dead center comprises a position of thepiston where the piston is nearest to a crankshaft of the variabledisplacement engine. In a first example of the method, the methodfurther includes where providing the spark event is a function ofin-cylinder pressure. A second example of the method optionally includesthe first example, and further includes wherein the spark event isprovided either once per an engine cycle, or twice per the engine cycle,where the engine cycle includes an exhaust stroke, an intake stroke, acompression stroke, and a power stroke. A third example of the methodoptionally includes any one or more or each of the first and secondexamples, and further includes wherein an ignition energy of the sparkevent is variable as a function of vehicle operating conditions. Afourth example of the method optionally includes any one or more or eachof the first through third examples, and further wherein deactivatingthe cylinder in the second mode by trapping the high-pressure charge inthe cylinder further comprises combusting a mixture of air and fuel inthe cylinder with the cylinder sealed from atmosphere, and thenmaintaining the cylinder sealed with combusted air and fuel trapped inthe cylinder. A fifth example of the method optionally includes any oneor more or each of the first through fourth examples, and furtherincludes wherein both the first mode and the second mode includesstopping injection of fuel provided to the cylinder, and wherein thesecond mode includes additionally stopping providing spark to thecylinder.

A system for a vehicle comprises a variable displacement engine,including a set of cylinders and where each cylinder is coupled to afuel injector and a spark plug, and where each cylinder includes apiston; and a controller, storing instructions in non-transitory memorythat, when executed, cause the controller to: in response to conditionsbeing met for deactivating a cylinder or a plurality of cylinders fromthe set of cylinders, determining whether to deactivate the cylinder orthe plurality of cylinders by trapping a vacuum in the cylinder or theplurality of cylinders, or to deactivate the cylinder or the pluralityof cylinders by trapping a high-pressure charge in the cylinder or theplurality of cylinders; and responsive to trapping the vacuum in thecylinder or the plurality of cylinders, providing spark when the pistonor pistons in the cylinder or the plurality of cylinders are within athreshold of bottom dead center, but not providing fuel to the cylinderor the plurality of cylinders while the cylinder or the plurality ofcylinders are deactivated, and responsive to trapping the high-pressurecharge in the cylinder or the plurality of cylinders, discontinuingproviding both spark and fuel to the cylinder or the plurality ofcylinders. A first example of the system further comprises a crankshaftcoupled to the variable displacement engine; a crankshaft positionsensor; a camshaft coupled to the variable displacement engine; acamshaft position sensor; and wherein the controller stores furtherinstructions to indicate, via one or more of the crankshaft sensorand/or the camshaft sensor, whether a piston or pistons of the cylinderor the plurality of the cylinders, respectively, are within thethreshold of bottom dead center, where the threshold of bottom deadcenter comprises a predetermined number of degrees from the bottom deadcenter position while the cylinder or the plurality of cylinders aredeactivated via trapping the vacuum, and where responsive to the pistonor pistons being within the threshold of bottom dead center position,providing spark via the spark plug. A second example of the systemoptionally includes the first example, and further comprises an oilquality sensor; and wherein the controller stores further instructionsto determine to deactivate the cylinder or the plurality of cylinders bytrapping the vacuum in response to an indication that an oil quality isgreater than an oil quality threshold, and to deactivate the cylinder orthe plurality of cylinders by trapping the high-pressure charge inresponse to an indication that the oil quality is lower than the oilquality threshold.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method, comprising: reducing fouling of aspark plug in a cylinder of an engine configured to propel a vehicle byproviding a spark to the cylinder after the cylinder has beendeactivated, where the spark is provided when a piston coupled to thecylinder is within a threshold of bottom dead center.
 2. The method ofclaim 1, where bottom dead center comprises a position of the pistonwhere the piston is nearest to a crankshaft of the engine.
 3. The methodof claim 1, wherein the threshold of bottom dead center includes thepiston being within a predetermined number of degrees from bottom deadcenter, and where the predetermined number of degrees comprises withinfive degrees or less of bottom dead center, within ten degrees or lessof bottom dead center, or within twenty degrees or less of bottom deadcenter.
 4. The method of claim 1, wherein the engine comprises avariable displacement engine.
 5. The method of claim 1, whereinproviding the spark to the cylinder after the cylinder has beendeactivated occurs in response to the cylinder being deactivated viatrapping a negative pressure with respect to atmospheric pressure in thecylinder at deactivation.
 6. The method of claim 5, wherein trapping thenegative pressure at deactivation includes exhausting a combustedmixture of air and fuel to an exhaust system of the engine, and thensealing the cylinder from atmosphere.
 7. The method of claim 1, whereindeactivating the cylinder includes stopping providing a fuel to thecylinder.
 8. The method of claim 1, wherein under conditions where aplurality of cylinders are selected for deactivation, providing spark tothe plurality of cylinders in response to deactivation of the pluralityof cylinders, at the predefined position of a plurality of pistonscoupled to the plurality of cylinders.
 9. The method of claim 1, whereina spark ignition energy comprising the spark provided to the cylinderafter deactivation of the cylinder is variable.
 10. The method of claim9, further comprising increasing the spark ignition energy after apredetermined number of spark events while the cylinder is deactivated.11. The method of claim 1, wherein a spark frequency of the sparkprovided to the cylinder is variable as a function of vehicle operatingconditions.
 12. A method, comprising: in a first operating condition ofa vehicle propelled by a variable displacement engine, including anindication that an oil quality of an oil utilized for cooling,lubrication and/or cleaning of the variable displacement engine isgreater than an oil quality threshold, operating the vehicle in a firstmode that includes selectively deactivating a cylinder of the variabledisplacement engine by trapping a vacuum in the cylinder; in a secondoperating condition of the vehicle, including an indication that the oilquality of the oil is lower than the oil quality threshold, operatingthe vehicle in the second mode that includes selectively deactivatingthe cylinder by trapping a high-pressure charge in the cylinder; andwhere operating the vehicle in the first mode further comprises,subsequent to deactivating the cylinder, providing a spark event to thecylinder when a piston coupled to the cylinder is within a threshold ofbottom dead center, where bottom dead center comprises a position of thepiston where the piston is nearest to a crankshaft of the variabledisplacement engine.
 13. The method of claim 12, where providing thespark event is a function of in-cylinder pressure.
 14. The method ofclaim 12, wherein the spark event is provided either once per an enginecycle, or twice per the engine cycle, where the engine cycle includes anexhaust stroke, an intake stroke, a compression stroke, and a powerstroke; and wherein each spark event includes one or more strikes of anignition coil of a spark plug configured to provide the spark event. 15.The method of claim 12, wherein an ignition energy of the spark event isvariable as a function of vehicle operating conditions.
 16. The methodof claim 12, wherein deactivating the cylinder in the second mode bytrapping the high-pressure charge in the cylinder further comprisescombusting a mixture of air and fuel in the cylinder with the cylindersealed from atmosphere, and then maintaining the cylinder sealed withcombusted air and fuel trapped in the cylinder.
 17. The method of claim12, wherein both the first mode and the second mode includes stoppinginjection of fuel provided to the cylinder, and wherein the second modeincludes additionally stopping providing spark to the cylinder.
 18. Asystem for a vehicle, comprising: a variable displacement engine,including a set of cylinders and where each cylinder is coupled to afuel injector and a spark plug, and where each cylinder includes apiston; and a controller, storing instructions in non-transitory memorythat, when executed, cause the controller to: in response to conditionsbeing met for deactivating a cylinder or a plurality of cylinders fromthe set of cylinders, determining whether to deactivate the cylinder orthe plurality of cylinders by trapping a vacuum in the cylinder or theplurality of cylinders, or to deactivate the cylinder or the pluralityof cylinders by trapping a high-pressure charge in the cylinder or theplurality of cylinders; and responsive to trapping the vacuum in thecylinder or the plurality of cylinders, providing spark when the pistonor pistons in the cylinder or the plurality of cylinders are within athreshold of bottom dead center, but not providing fuel to the cylinderor the plurality of cylinders while the cylinder or the plurality ofcylinders are deactivated, and responsive to trapping the high-pressurecharge in the cylinder or the plurality of cylinders, discontinuingproviding both spark and fuel to the cylinder or the plurality ofcylinders.
 19. The system of claim 18, further comprising: a crankshaftcoupled to the variable displacement engine; a crankshaft positionsensor; a camshaft coupled to the variable displacement engine; acamshaft position sensor; and wherein the controller stores furtherinstructions to indicate, via one or more of the crankshaft sensorand/or the camshaft sensor, whether a piston or pistons of the cylinderor the plurality of the cylinders, respectively, are within thethreshold of bottom dead center, where the threshold of bottom deadcenter comprises a predetermined number of degrees from the bottom deadcenter position while the cylinder or the plurality of cylinders aredeactivated via trapping the vacuum, and where responsive to the pistonor pistons being within the threshold of bottom dead center position,providing spark via the spark plug.
 20. The system of claim 18, furthercomprising: an oil quality sensor; and wherein the controller storesfurther instructions to determine to deactivate the cylinder or theplurality of cylinders by trapping the vacuum in response to anindication that an oil quality is greater than an oil quality threshold,and to deactivate the cylinder or the plurality of cylinders by trappingthe high-pressure charge in response to an indication that the oilquality is lower than the oil quality threshold.